Khan commissioned a series of impact papers to determine the potential impact of different Brexit scenarios on key sectors of the United Kingdom economy after Brexit secretary David Davis said the government had not done so. The hit to London is calculated at 2%.
The analysis concludes that the harder the Brexit we end up with, the bigger the potential impact on jobs, growth and living standards.
Sadiq Khan accused the British Government of a "total lack of preparation" on the consequences of Brexit, calling on it to change its negotiation position and agree to keep the country in the single market and customs union.
The report also shows that London could suffer much less from Brexit than the rest of the country - increasing "geographic inequalities" across the UK.
Cambridge Econometrics, an economics consultancy, looked at five different Brexit scenarios, from the hardest to the softest form of Brexit, and broke down the economic impact on nine industries, from construction to finance. Ministers are fast running out of time to turn the negotiations around.
The research suggests 500,000 jobs could be lost under a "hard Brexit" scenario, with 87,000 at risk in London.
It also notes that while post-Brexit restrictions on immigration could reduce the number of overseas workers available to employers: "London residents who were unemployed or inactive may be employed following migration restrictions because there is less competition for jobs".
"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".
International Trade Secretary Liam Fox called the report into the impact of Brexit "anything other than cataclysmic".
The firm, which has offices in Brussels, is managed by Philip Summerton, who regularly retweets European Union loyalists such as Chuka Umunna MP and former Remain campaign director Will Straw. "I don't believe that we will necessarily lose our share of market".