A study commissioned by London Mayor Sadiq Khan shows that nearly half a million jobs are under threat if Britain fails to strike a deal on future relations with the European Union before it leaves the bloc.
According to the analysis, London's professional and financial services would be the worst hit by a no-deal hard Brexit, with 29,000 fewer jobs by 2030 than if Britain remained in the Single Market and Customs Union.
Brexit was the main reason for a 37 percent drop in new jobs available in London's financial sector last month, according to a report from recruiting firm Morgan McKinley. Meanwhile, the financial impact of a hard Brexit would be the loss of almost £50 billion in United Kingdom -wide investment over the next 12 years.
Discussing the newly published Brexit impact reports he commissioned, Mr Khan said: "I'm not in a state of denial, I accept we are probably leaving the European Union".
The analysis also shows that London's economy would suffer significantly less from Brexit than the rest of the UK.
Ben Gardiner from Cambridge Econometrics said: "Our analysis is particularly valuable to local leaders because it indicates the potential impact on employment and output of Brexit under a range of scenarios, which is necessary given the uncertainty surrounding the final outcome of negotiations".
The warning was issued in new independent economic analysis commissioned by the Mayor of London, Sadiq Khan. Ministers are fast running out of time to turn the negotiations around.
But even a softer Brexit and remaining in the Single Market but leaving the Customs Union could cost thousands of jobs. "It is clear that a no-deal, hard Brexit without a transitional deal will place all this under threat". He said the "complete lack of preparation" is "irresponsible", "astonishing" and that the Tories were putting party politics ahead of the national interest. The analysis does however highlight the scale of the comparative risks associated with each scenario and potential outcome from the negotiations.
Other scenarios include continued membership of either the customs union or the single market, a transition deal phasing out membership, and a situation in which there is no transition deal, no membership of either the single market or customs union and no preferential trade agreement.
A stand-off between Britain and the European Union over future access to the single market for London's financial services industry is shaping up to be one of the key Brexit battlegrounds before Britain is due to leave the bloc in March 2019.