In Chester Square, the exclusive London address that was once home to Margaret Thatcher, multimillion-pound stuccoed townhouses are proving a hard sell.

More than 20 luxury properties in the Belgravia postcode are on the market, says a buying agent. In nearby Montpelier Square in Knightsbridge, less than a 10-minute walk from Harrods department store, nine houses are on the open market.

Huge price reductions do not appear to be working either, with some homes lingering unsold for months and even years despite repeated reductions. One six-bedroom Chester Square townhouse has been on the market since 2022, despite its price being slashed by £4m – almost a quarter of its original £17.5m listing.

One possible reason for this luxury property glut has been echoing loudly in City boardrooms and the offices of Mayfair advisers in recent months: the world’s footloose super-rich are starting to lose interest in the UK, put off by Labour’s tax changes. After Vladimir Putin’s invasion of Ukraine in 2022 halted the flow of wealthy Russians, some claim Labour’s non-doms tax has sent the global elite fleeing the UK for cities such as Milan, Singapore, Geneva and Dubai.

At the heart of their complaint is the abolition of the centuries-old non-dom regime, which allowed wealthy foreign people to avoid paying tax on money they were earning outside the UK, and avoid paying inheritance tax on their global assets.

Such is the concern that Rachel Reeves is reportedly considering softening changes to the inheritance tax aspect of the non-doms clampdown. But that comes amid speculation about more tax rises in the autumn budget, after Labour’s U-turn on its welfare bill left a £5bn hole in the chancellor’s fiscal plan– with wealth taxes increasingly popular among some campaigners and the left of the party.

A colonial era relic

It was under the last Conservative government that Jeremy Hunt laid out plans to replace the 225-year-old non-doms system, a relic of Britain’s colonial era.

Introduced under King George III in 1799, it allowed subjects who had been born in Britain’s colonies to live in England without paying tax on their foreign rents and stocks so long as the money remained abroad.

After winning last year’s election, Labour went a step further by also exposing their overseas assets to the UK’s inheritance tax. The death duty is levied at a rate of 40% and, although it comes with a basket of allowances and exemptions, it is one of the highest in the world.

Under the new regime, non-doms’ foreign income and gains are subject to UK tax after four years rather than the previous 15. A new residence-based system means also that their global assets are subject to inheritance tax after 10 years.

It is this inheritance tax element that has been the “emotional trigger” for non-doms, tax experts and chief executives say. One financial services CEO said older wealthy clients in particular were relocating abroad to escape the death duty.

Several prominent non-dom departures have captured headlines: Shravin Bharti Mittal, an heir of one of India’s richest families; Nassef Sawiris, the Egyptian investor; and Richard Gnodde, a veteran Goldman Sachs banker.

One Indian non-dom, who has been living in the UK for the past five years, said she was considering moving her family to Switzerland as a result of the tax changes.

“We love England. We feel very much at home here,” she said. “We want to pay fair tax as members of society. But the biggest pain point was inheritance tax … it is not just ours, but my grandfather’s and my parents’ wealth that would now be taxed by the UK. That feels deeply unfair as the money was not made here.

“The current philosophical approach seems to be shrinking everyone’s pie instead of enlarging the pie, bringing more investment, employability and wealth to the country.”

Sean Cockburn, of the advisers Forvis Mazars, said while many non-doms were unhappy with the changes, most of his clients were staying in the country.

“There has been an acceptance of higher income and capital gains but the emotional trigger has been inheritance tax. That seems to be the motivator for those moving. But not everyone is leaving the UK entirely.

“Yes some people have left, some people are considering it, but some people have decided to stay and are broadly accepting of the new rules. In the media there have been very high-profile, very wealthy people leaving who receive a lot of coverage. I personally have not had many clients leaving.”

As well as Reeves considering a reversal of her decision to charge UK inheritance tax on global assets of non-doms, Nigel Farage has promised Reform UK would “bring back” wealthy foreigners who have left Britain by giving them a full exemption from taxes on their overseas assets in return for a once-a-decade £250,000 fee.

Is there really an exodus, and what might it cost?

The UK counted about 74,000 non-doms when the regime ended in April. After the government announced its changes to the tax policy, the Office for Budget Responsibility estimated it could lead to a 12% to 25% decrease in the population of non-doms without trusts.

Collectively they paid just under £9bn in tax in 2023, according to figures from HMRC. About £6bn of that came from income tax, £2.3bn from national insurance contributions and £400m from capital gains tax.

John-Paul Marks, the new permanent secretary and chief executive of HMRC, told MPs in June that official data would only start to come through in January 2027, when self-assessment tax returns were due.

Still, in the absence of official figures, reports with estimates have emerged, often commissioned by interested parties such as the investment migration company Henley & Partners, and campaign groups such as Land of Opportunity and Foreign Investors for Britain.

Research commissioned by Henley found the UK could lose a net 16,500 “dollar millionaires” this year, those with at least $1m (£736,000) in liquid investable wealth, which includes assets such as cash, bonds, stocks and gold. But the figures are disputed, with the campaign group Tax Justice Network criticising the report’s reliance on social media platforms, such as LinkedIn, as a measure of where millionaires live or reside. A spokesperson for Henley & Partners said the report relied on multiple sources, not just LinkedIn.

A spokesperson for New World Wealth, the company that conducted the research, said the report also used sources such as investment migration programme statistics from across the world, its in-house database, company registers and property registers, among others.

Stuart Adam, a senior economist at the Institute for Fiscal Studies, a thinktank, emphasised that until official data from the UK government arrives, there simply is not enough information to draw conclusions about how many non-doms have left, or would leave as a result of the changes.

“Scraping people’s LinkedIn pages and their changed location is extrapolating massively,” he said. “A change in location may not correspond with a change in tax residence.

“I have not seen anything that could qualify as proper evidence. It is a hot topic so people will put out what they can. But it will be one or two years, or even longer, when data becomes available.”

A study co-authored by Arun Advani, a tax economist at the University of Warwick, found previous patterns would suggest the loss of the tax break will result in a “significant” but “temporary” exodus.

But he has said he expects a bigger backlash this time, particularly because of the change to inheritance tax rules. Non-doms, who previously did not have to pay inheritance tax on their global assets (including businesses they had built in their homeland), now have to pay the levy on these assets if they have been resident in the UK for 10 of the past 20 tax years.

“It was always a mistake to have the IHT rate for foreigners jump from 0% to 40% overnight when they get to 10 years in the UK,” he told Bloomberg.

The OBR had forecast that the changes to the non-dom regime would generate £33.8bn in revenue for the Treasury over the next five years. However, there is considerable uncertainty around those numbers.

A report from the Centre for Economics and Business Research found that if a quarter of non-doms left the UK, the net gain to the Treasury would be zero. That research was commissioned by Andrew Barclay, the co-founder of the property platform Yopa, grandson of one of the billionaire Barclay brothers.

Barclay now runs the Land of Opportunity Campaign, a lobbying effort that intends to recreate Britain’s economy in the image of the US.

The non-dom lobby group Foreign Investors for Britain has also been highly active in the area, with research conducted by Oxford Economics on its behalf finding that nearly two-thirds of non-doms were planning to leave the UK or considering doing so because of the changes. That was based on surveys responded to by 73 non-doms and 42 tax advisers. It also found that inheritance tax changes was a key motivator for 83% of non-doms in any relocation decision.

Ed Bussey, the chief executive of Oxford Sciences, a builder of UK technology spin-outs from Oxford University, said he was increasingly hearing from non-UK investors, who have historically funded companies in the UK, but who are now leaving the country because of the changes to inheritance tax.

“While they don’t want to leave they can’t justify having their worldwide assets – which they often grew before coming to the UK – now being taxed at 40%, while other European and Middle East countries are charging little or no inheritance tax,” he said.

“There is simply not enough UK domiciled investment capital to fund the innovation-led companies that we’re building and the high dependency on foreign capital is critical.”

He said the same issue was also deterring international entrepreneurs from coming to the UK to build their companies.

“We should be rolling out the red carpet to this highly sought-after global talent pool, not ‘incentivising’ to go to Italy, Greece or Dubai instead – all of which are now seeing substantial inflows of the investment capital that we’ve lost,” he said.

Donald Trump has certainly taken the view that wealthy individuals should be welcomed with open arms. The president has drawn up plans for a “gold card” that rich foreigners can buy for $5m that would grant them permanent US residency.

But Paul Donovan, the chief economist at the wealth management arm of the Swiss bank UBS, added that the population of truly “nomadic” wealth owners is “perhaps smaller than popularly supposed”.

“Certainly in conversations with UK clients, the issue of changing tax rules has come up more often, as you would expect,” he said. “To date there is very little evidence to suggest the idea of an exodus.

“You will always have high-profile nomadic wealth owners who will move and change their location.”

More tax please

For all the noisy departures, there are lower-profile non-doms who wish to stay in the UK, prizing its robust rule of law, elite schools system and world class museums, galleries and restaurants.

Giorgiana Notarbartolo, an impact investor who helps to run her family office, is one former non-dom who plans to stay in the country. Born in Italy, she has been in the UK since 2016. “I have been uncomfortable not paying tax off the wealth I make in Italy,” said Notarbartolo, a member of Patriotic Millionaires. “Who wants to raise their kids in a two-tier system?

“There are many single millionaires, if that, who are also non-doms. Some are staying and some are leaving, but not all are citing tax as their main reason, it’s something that might tip them off the edge if they were thinking about leaving anyway. Education and higher private school fees are a big reason.”

Paolo Fresia, also native to Italy and an impact investor who lives in London, said he has been “appalled by the media coverage” on the subject. In fact, he said, although he claimed non-dom status, he felt “a bit guilty” and now felt “relief” that the system was no longer in place.

“I first moved here for educational reasons, not for tax. There are so many reasons to be here, not just tax, but education, meritocracy and the rule of law. There is even a new four-year regime for people.”

“None of my friends or colleagues are moving,” added Fresia, also a member of Patriotic Millionaires. “Some parents of friends are leaving but those are the ones who are coming to the end of their lives, do not work or invest and were already thinking about leaving. I am happy to pay tax here.”