Mr Barnier said there was still a possibility of a trade deal not being struck by the end of 2020.
There are fears that leaving the EU without a deal in place could hit imports of medicine.
The Prime Minister must outline his Brexit plans by the end of September.
The document details how the Government is planning for a no-deal Brexit.
All stages of the EU Withdrawal Bill will be completed by 5pm on Friday.
The Prime Minister is now pushing for an early general election.
Ms Miller said the PM was 'hijacking the Queen's prerogative power'.
Any petition that secures 100,000 signatures forces a debate in Parliament.