The mayor of London Sadiq Khan commissioned a set of economic studies of the impact of different Brexit outcomes on regions and nine key sectors after Brexit Secretary David Davis said the Government had not done such work.
The report also argues that London could suffer much less from Brexit than the rest of the country, thereby increasing geographic inequalities across the UK.
The analysis commissioned by Cambridge Econometrics, focused on five possible outcomes after leaving the European Union, ranging from a near status quo scenario to leaving on World Trade Organisation terms without a transition deal.
The professional and financial services areas would be worst hit with some 119,000 fewer jobs nationally, according to the study from the Mayor of London Sadiq Khan. Our dedicated coverage of Labour's policies and personalities, internal debates, selections and elections relies on donations from our readers.More news: White House personal cell phone ban starts next week
"A no-deal Brexit runs the risk of completely undermining the growth and development of recent years and could see London fall way down the league table of global science and tech hubs".
The research also suggests 500,000 jobs could be lost under a "hard Brexit" scenario, with 87,000 at risk in London.
The Labour mayor was a strong supporter of the Remain campaign and has since vigorously argued for the United Kingdom to stay in the EU's single market and customs union, or for London to be granted its own deal, especially on maintaining rules on banking and financial services.
He added: "The analysis concludes that the harder the Brexit we end up with, the bigger the potential impact on jobs, growth and living standards".More news: Trump author defends book as president claims it is 'lies'
Mr Khan is warning that with just 10 months to go, time is running out. He said the "complete lack of preparation" is "irresponsible", "astonishing" and that the Tories were putting party politics ahead of the national interest.
"This new analysis shows why the Government should now change its approach and negotiate a deal that enables us to remain in both the EU Single Market and the EU Customs Union".
The report compares four possible post-Brexit scenarios to the option of maintaining the status quo - already ruled out by the British government - of staying in the European single market and customs union.
Both the London mayor and Cambridge Econometrics admit that this analysis is not a precise forecast of what will happen.More news: National Football League looking into Raiders hiring process for head coach
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