It is believed the bill has been calculated to include the obligation for Britain to pay into the EU budget until the end of 2020.
Other associated costs include outstanding pensions liabilities, and payments in connection with loan guarantees.
However, a Downing Street spokesman insisted that any future costs to Britain will be ‘open to negotiation.’
The figure comes as the Prime Minister was in Brussels yesterday warning a ‘smooth and orderly Brexit’ was in everyone’s interest amid claims the talks could take a decade.
In a highly symbolic event, Mrs May’s counterparts from the 27 other EU nations were also meeting without the presence of the UK’s Prime Minister in order to agree how to approach the Brexit talks.
Following the summit, Mrs May departed looking glum without answering questions on Brexit following the end of the formal European Council summit, leaving the other leaders behind.