Bambridge, which specialises in providing services to American expats, predicts that 10-15% of Britain’s 225,000 US expats would be impacted by the US president’s plan to scrap the net investment income tax, also known as the Medicare tax.

Americans living abroad are required to make annual filings with the country’s tax authority, the Internal Revenue Service (IRS).

Meanwhile, that and other requirements such as the foreign account tax compliance act (FATCA) and the report of foreign bank and financial accounts (FBAR) has caused as many as 40% of Americans living outside the US to consider renouncing their citizenship, according to US firm Greenback Expat Tax Services, which surveyed 2,100 US expats.

FATCA sees foreign financial institutions report on the foreign assets held by their US account holders, while FBAR requires American holders of accounts outside the US to declare them to the IRS.

Half of those who are either planning or considering giving up their citizenship say the primary reason is the burden of US tax rules.

However, despite those frustrations, Bambridge expects the repeal of the investement income tax to save wealthier US expats between $500 and $1000 each and up to an extra $34m will be freed up for US high-fliers to pump back into the UK economy. London, as home to the UK’s highest concentration of wealthy American expats, would receive a disproportionately large boost from the windfall.

Since January 2013, high-earning US citizens have been subject to a 3.8% surtax on investments when their net income is above $200,000 (for individuals) and $250,000 for married couples.

The additional charge is one of the main reasons some UK-based American expats end up having to pay US income tax in addition to UK tax, because US citizens cannot offset their UK tax credits against the additional tax charge.

The repeal of the Medicare tax is one of a raft of tax reforms announced by President Trump, which in typically understated style he has described as ‘the biggest in a generation’.

The plan was approved in May by the US House of Representatives but still needs the green light from the Senate before to become law.

Alistair Bambridge, senior partner at Bambridge Accountants, said: ‘Tax cuts are a big priority for President Trump – and while it’s unlikely he set out specifically to help Britain’s US expat community, they will emerge as big winners if the Senate gives this plan the nod.

‘While the status of EU citizens in a post-Brexit Britain remains unclear, life for many in Britain’s US expat community could be about to get a little easier. The repeal of this surtax will spare thousands of Americans living here the bizarre and costly experience of having to pay income tax to both London and Washington.’