Analysts from three City of London financial institutions expect the cost of Theresa May's hard Brexit to add up to between 5 per cent and 10 per cent of GDP by 2030.

In today's money that's equivalent to between £100bn and £200bn.

This is an estimate of the loss of GDP relative to where the economy would have been without Brexit.

Theresa May: UK left the EU to embrace the world

Last week Theresa May revealed that the Government expects to pull the UK out of the single market and customs union and establish a free-trade deal with the rest of the European Union instead.

In a note to clients, Rob Wood, chief UK economist at the Bank of America, stressed that there was inherent uncertainty over the long-term impact of such a Brexit, but said that "evidence suggests" the costs will be "of the order of 5-10 per cent of GDP over perhaps 15 years".

That view is broadly echoed by Kallum Pickering, UK economist of Berenberg bank, who estimates that lower migration, trade and investment between the UK and Europe due to Britain leaving the EU single market could reduce the UK's potential growth rate from 1.8 per cent per year from its pre-referendum rate of 2.2 per cent.

That implies a GDP loss due to Brexit by 2030 of roughly 5.5 per cent.

Likewise, Simon French, chief economist of the broker Panmure Gordon, expects Brexit to reduce the UK's trend growth rate from 2.3 per cent to 1.9 per cent from 2020 onwards.

That also implies a hit to GDP of around 5 per cent.

"This mainly hinges on a reduction in long-term net migration to 105,000 a year and sustained trade diversion through non-tariff barrier differentiation and heightened administrative burdens from a loss of customs union," Mr French said.

The City economists' estimates are in line with those of the Treasury's pre-referendum forecast for the damage of a Brexit in which the UK manages to establish a basic Canada-style free-trade deal with the rest of the EU.

This predicted a 6.2 per cent hit to GDP by 2030.

Other independent forecasts from the likes of the National Institute of Economic and Social Research (Niesr), the accountancy firm PwC and the consultancy Oxford Economics of such a scenario were for a smaller-impact GDP, although they were all still negative.

Samuel Tombs UK economist of Pantheon Macroeconomics said he found the Treasury's original work on the long-term impact "plausible".

Despite the better-than-expected short-term performance of the economy since last June's referendum most economists have not altered their view that Brexit will ultimately be damaging for the UK economy.

Business news: In pictures Show all 13 1 /13 Business news: In pictures Business news: In pictures Flybe collapses Airline Flybe has collapsed. All future flights on the Exeter-based airline have been cancelled – leaving more than 2,300 staff facing an uncertain future, and wrecking the travel plans of hundreds of thousands of passengers. The chief executive, Mark Anderson, said: “Europe’s largest independent regional airline has been unable to overcome significant funding challenges to its business. AFP via Getty Business news: In pictures Future product placement will be 'tailored to individual viewers' Marketing executives say that product placement in films and televison shows on streaming services such as Netflix may be tailored to individuals in future. For instance, if data shows that a viewer is a fan of pepsi, a billboard in the background of a shot would host an advert for pepsi, while for a viewer known to have different tastes it could be for Coca-Cola Paramount Business news: In pictures Corbyn wishes Amazon a happy birthday In a card sent to Amazon CEO Jeff Bezos on the company's 25th birthday, Labour leader Jeremy Corbyn writes: "You owe the British people millions in taxes that pay for the public services that we all rely on. Please pay your fair share" Business news: In pictures No deal, no tariffs The government has announced that it would slash almost all tariffs in the event of a no-deal Brexit. Notable exceptions include cars and meat, which will see tariffs in place to protect British farmers Getty Business news: In pictures Fingerprint payment NatWest is trialling a new bank card that will allow people to touch their hand to the card when paying rather than typing in a PIN number. The card will work by recognising the user's fingerprint NatWest/PA Wire Business news: In pictures Mahabis bust High-end slipper retailer Mahabis has gone into administration. 2 Jan 2019 Mahabis Business news: In pictures Costa Cola Coca-Cola has paid £3.9bn for Costa Coffee. A cafe chain is a new venture for the global soft drinks giant PA Business news: In pictures RIP Payday Loans A funeral procession for payday loans was held in London on September 2. The future of pay day lenders is in doubt after Wonga, Britain's biggest, went into administration on August 30 PA Business news: In pictures Musk irks investors and directors Elon Musk has concluded that Tesla will remain public. Investors and company directors were angry at Musk for tweeting unexpectedly that he was considering taking Tesla private and share prices had taken a tumble in the following weeks Getty Business news: In pictures Jaguar warning Iconic British car maker Jaguar Land Rover warned on July 5, 2018 that a "bad" Brexit deal could jeopardise planned investment of more than $100 billion, upping corporate pressure as the government heads into crucial talks AFP/Getty Business news: In pictures Spotif-IPO Spotify traded publically for the first time on the New York Stock Exchange on Tuesday. However, the company isn't issuing shares, but rather, shares held by Spotify's private investors will be sold AFP/Getty Business news: In pictures French blue passports The deadline to award a contract to make blue British passports after Brexit has been extended by two weeks following a request by bidder De La Rue. The move comes after anger at the announcement British passports would be produced by Franco-Dutch firm Gemalto when De La Rue’s contract ends in July. The British firm said Gemalto was chosen only because it undercut the competition, but the UK company also admitted that it was not the cheapest choice in the tendering process. Business news: In pictures Beast from the east economic impact The Beast from the East wiped £4m off of Flybe’s revenues due to flight cancellations, airport closures and delays, according to the budget airline’s estimates. Flybe said it cancelled 994 flights in the three months to 31 March, compared to 372 in the same period last year.

A Financial Times poll of 120 economists before the referendum vote found that three quarters thought Brexit would do long-term harm. A follow-up poll earlier this month found that half had not changed their view, while 40 per cent had become more pessimistic.

Just 13 per cent were now more optimistic than previously.

Some City economists say that even if Theresa May successfully concludes the free-trade agreement (FTA) she says she wants, the UK's freedom for manoeuvre on commerce will be much more restricted than it was before.