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Brexit has cost the British economy £550 million a week since the referendum, a report has found.

Standard & Poor's suggested that since the June 2016 vote, 3 per cent has been shaved off GDP.

That equates to "forgone economic activity" of £6.6 billion in each of the 10 quarters since the referendum, or £66 billion, the credit ratings agency said.

The S&P report comes as MPs remain in deadlock over Britain's divorce terms, with Theresa May appealing to Jeremy Corbyn to help her break the impasse.

The group said the UK's economic performance has suffered from the "mere anticipation" of Brexit.

"The most visible effect has been the depreciation of the British pound, which triggered an increase in inflation. The ultimate result was to erode household spending power,” the report said.

"Household spending would have been considerably stronger - in line with GDP - had the referendum not occurred," S&P said in its publication, Countdown To Brexit: What Might Have Been For The UK Economy.

London People's Vote march: In Pictures 38 show all London People's Vote march: In Pictures 1/38 EPA 2/38 An EU supporter with her face painted REUTERS 3/38 PA 4/38 AFP/Getty Images 5/38 REUTERS 6/38 EPA 7/38 A demonstrator carries a dog on his shoulders AP 8/38 An EU supporter carries a child on his shoulders, calling on the government to give Britons a vote on the final Brexit deal REUTERS 9/38 PA 10/38 REUTERS 11/38 EU supporters dressed in costumes REUTERS 12/38 EPA 13/38 Sir Vince Cable in attendance PA 14/38 A demonstrator holds a holds a poster AP 15/38 EPA 16/38 An EU supporter with the EU flag painted on her face, REUTERS 17/38 Getty Images 18/38 A demonstrator leads a dog wearing a suit in the EU colors during a Peoples Vote AP 19/38 An EU supporter takes a selfie with a sticker on his nose REUTERS 20/38 Demonstrators pull a cart with a doll AP 21/38 Katie Walton 22/38 Placards stand against a wall Getty Images 23/38 Anti-Brexit campaigners before they take part in the People's Vote March PA 24/38 Katie Walton 25/38 Getty Images 26/38 Getty Images 27/38 A demonstrator and her dog wait for the start of a Peoples Vote anti-Brexit march in London AP 28/38 REUTERS 29/38 Demonstrators on their way from London Victoria Jacob Jarvis 30/38 Independent Group MPs Chuka Umunna and Anna Soubry have a selfie taken with Tracey Ullman PA 31/38 REUTERS 32/38 The march took place in central London REUTERS 33/38 An anti-Brexit banner is unfurled from Westminster PA 34/38 A demonstrator holds a dog on a leash as people start gathering for a Peoples Vote anti-Brexit march in London AP 35/38 Anti-Brexit campaigners in Park Lane PA 36/38 Demonstrators carry posters during a Peoples Vote AP 37/38 nti-Brexit badges are seen Getty Images 38/38 Getty Images 1/38 EPA 2/38 An EU supporter with her face painted REUTERS 3/38 PA 4/38 AFP/Getty Images 5/38 REUTERS 6/38 EPA 7/38 A demonstrator carries a dog on his shoulders AP 8/38 An EU supporter carries a child on his shoulders, calling on the government to give Britons a vote on the final Brexit deal REUTERS 9/38 PA 10/38 REUTERS 11/38 EU supporters dressed in costumes REUTERS 12/38 EPA 13/38 Sir Vince Cable in attendance PA 14/38 A demonstrator holds a holds a poster AP 15/38 EPA 16/38 An EU supporter with the EU flag painted on her face, REUTERS 17/38 Getty Images 18/38 A demonstrator leads a dog wearing a suit in the EU colors during a Peoples Vote AP 19/38 An EU supporter takes a selfie with a sticker on his nose REUTERS 20/38 Demonstrators pull a cart with a doll AP 21/38 Katie Walton 22/38 Placards stand against a wall Getty Images 23/38 Anti-Brexit campaigners before they take part in the People's Vote March PA 24/38 Katie Walton 25/38 Getty Images 26/38 Getty Images 27/38 A demonstrator and her dog wait for the start of a Peoples Vote anti-Brexit march in London AP 28/38 REUTERS 29/38 Demonstrators on their way from London Victoria Jacob Jarvis 30/38 Independent Group MPs Chuka Umunna and Anna Soubry have a selfie taken with Tracey Ullman PA 31/38 REUTERS 32/38 The march took place in central London REUTERS 33/38 An anti-Brexit banner is unfurled from Westminster PA 34/38 A demonstrator holds a dog on a leash as people start gathering for a Peoples Vote anti-Brexit march in London AP 35/38 Anti-Brexit campaigners in Park Lane PA 36/38 Demonstrators carry posters during a Peoples Vote AP 37/38 nti-Brexit badges are seen Getty Images 38/38 Getty Images

It added that external trade did not see any significant boost from the pound's collapse, contrary to claims from leading Brexit proponents that exports would be boosted.

S&P senior economist Boris Glass said: "Uncertainty over the shape and form Brexit will take has increasingly paralysed any forward-looking decision making.

"This is reflected in particular in a contraction of business investment in 2018."

The analysis, based on the Doppelganger economic method, also shows that British-based businesses have "ventured well beyond the point of no return", which will hammer the economy even harder.

"They have reorganised their business structure to comply with regulation and to safeguard unimpeded EU market access. This will also dampen growth while the economy adjusts to the new business environment after Brexit, whether there is a deal or not."

The findings are the latest in a series of Brexit impact assessments.

Investment banking giant Goldman Sachs estimated that £600 million a week as been lost because of Brexit, and the Bank of England suggested a figure of around £40 billion per year, or £800 million per week.

All three figures are significantly higher than the £350 million a week the Leave campaign's bus claimed would be saved by Britain.