'Boris Johnson has written to the EU, saying that the Irish backstop must be dropped if a deal is to take place.
The letter comes just hours after Downing Street said freedom of movement between the UK and the EU will end on Brexit day, if Britain leaves the bloc with no-deal.
'However, following conversations between the Prime Minister and the Irish premier, free movement between the UK and Ireland will still continue.
In his letter to EU Council President Donald Tusk outlining his opposition to the Irish backstop element of the Withdrawal Agreement, Mr Johnson said his Government's "highest priority" remains to leave with a deal, but this could not happen if the backstop remained part of the Withdrawal Agreement.
— Boris Johnson (@BorisJohnson Aug 19th 2019
He added: "It is anti-democratic and inconsistent with the sovereignty of the UK as a state.
"The backstop locks the UK, potentially indefinitely, into an international treaty which will bind us into a customs union and which applies large areas of single market legislation in Northern Ireland.
"The treaty provides no sovereign means of exiting unilaterally and affords the people of Northern Ireland no influence over the legislation which applies to them."
Mr Johnson said he is committed to ensuring there is no return to a hard border on the island of Ireland.
He proposed "flexible and creative solutions to the unique circumstances on the island of Ireland".
He added: "I propose that the backstop should be replaced with a commitment to put in place such arrangements as far as possible before the end of the transition period, as part of the future relationship.
"I also recognise that there will need to be a degree of confidence about what would happen if these arrangements were not all fully in place at the end of that period.
"We are ready to look constructively and flexibly at what commitments might help, consistent of course with the principles set out in this letter."
Mr Johnson acknowledged that "time is very short" but said: "The UK is ready to move quickly, and, given the degree of common ground already, I hope that the EU will be ready to do likewise."
Read more: Boris Johnson says Irish backstop must be dropped if UK is to leave EU with a deal