"The introduction of WTO tariffs and a devaluation of the pound in case of a hard Brexit would shrink auto sales and manufacturing in the United Kingdom, directly impacting German vehicle suppliers", the report said.
Even softer Brexit scenarios, it is argued, like the United Kingdom remaining in the single market, but leaving the customs union after a transition period, could still result in a 176,000 fewer jobs.
The British government on Thursday ruled out paying the European Union to access the single market after leaving the bloc, as Prime Minister Theresa May tried to reassure finance sector players over Brexit.
As part of the study, five scenarios were examined, from the United Kingdom remaining in the single market and customs union, to leaving both, failing to get a free trade agreement or a transition period, and invoking World Trade Organisation rules.
Government figures were reportedly looking into a "tailor-made" trade deal, with the United Kingdom remaining tied to the bloc's financial markets, The Times claimed.
Mrs. May has already said the United Kingdom will meet "financial obligations" to the bloc, believed to total around £20 billion, and will continue paying into the bloc's annual budget for the agreed two-year so-called Brexit "transition period".
BREXIT could cost the United Kingdom almost 500,000 jobs in a worst-case scenario, according to a study published today which was commissioned by the mayor of London.
European diplomats had earlier indicated a Brexit trade deal could include financial services if Britain is willing to pay "for access" and follows EU law.
"The Prime Minister gave an overview of the UK's position and updated on Brexit negotiations -- including the UK's aim to agree an implementation period by the end of March", he added.