Confidential documents that “reflect the ideas the UK has put forward” on Brexit have been shared with the EU, the UK government has said.
Ministers will table “formal written solutions when we are ready” and not to an “artificial deadline”, it added.
This comes after Finland’s prime minister said Boris Johnson had 12 days to set out his Brexit plans to the EU.
The European Commission said documents had been received and technical talks were taking place.
The commission’s chief spokesperson, Mina Andreeva, also confirmed there would be talks at a political level at a meeting on Friday between the EU’s chief negotiator, Michel Barnier, and Brexit Secretary Stephen Barclay.
The technical discussions were on some aspects of rules relating to customs and manufactured goods, as well as sanitary rules and phytosanitary rules – which relate to the health of plants – she said.
Prime Minister Boris Johnson has said he wants to leave the EU, preferably with a deal, on 31 October and has urged the EU to scrap the backstop in the withdrawal agreement reached by predecessor Theresa May.
The backstop is the controversial policy aimed at preventing the return of a hard border on the island of Ireland and it was a key sticking point in Mrs May’s attempts to get Parliament to back her plan.
The EU has asked for alternative suggestions and had criticised the UK for not putting any plans in writing.
A UK government statement said: “We have now shared in written form a series of confidential technical non-papers which reflect the ideas the UK has been putting forward.
“We will table formal written solutions when we are ready, not according to an artificial deadline, and when the EU is clear that it will engage constructively on them as a replacement for the backstop.”
This development was not in response to the remarks from Finland’s prime minister, Antti Rinne, a government source said, adding that the documents had been submitted “in the last week”.
Earlier, Mr Rinne said he and French President Emmanuel Macron agreed the UK needed to produce the proposals in writing by the end of September, adding if not, “then it’s over”.
Finland currently holds the EU’s rotating presidency.
A French government official said the deadline was “not at all a new proposal” and added: “If we don’t get the proposals before the end of September, we will not have enough time to discuss them before the summit in October.”
Meanwhile, speaking during a visit to Spain, Mr Barclay said “a rigid approach” was “no way to progress a deal” and said the responsibility “sits with both sides to find a solution”.
He said the prime minister had shown he was willing to be “creative and flexible” by considering an all-Ireland approach to plant and animal checks and he said a negotiating partner should itself be “willing to compromise”.
Elsewhere, Ireland’s deputy prime minister Simon Coveney said there was “still a big gap” between what the UK government wanted and what Ireland and the EU needed, in terms of getting a deal.
“In order to close that gap we need to get credible proposals from the British government which we simply haven’t received yet,” he said.
The sending of the documents to the EU comes as the legal battle over the suspension of the UK Parliament is in its third day at the UK’s Supreme Court.
The UK government is arguing the decision to prorogue Parliament was a political matter and not for the courts to “design a set of rules” around it.
But campaigners say the move was used “for an improper purpose” – to stop MPs scrutinising Mr Johnson’s plans in the run up to Brexit on 31 October.
The prime minister prorogued Parliament earlier this month for five weeks, with MPs not scheduled to return until 14 October.