The UK has told Brussels to be flexible and willing to compromise in Brexit talks as Boris Johnson came under further pressure to produce his plan for a deal.

Finnish Prime Minister Antti Rinne, following talks in Paris with French President Emmanuel Macron, said Britain should outline its Brexit plans to the EU by the end of September.

But Brexit Secretary Stephen Barclay warned the European Union against a “rigid” approach and suggested the final details of an alternative to the Irish backstop may not need to be resolved until the end of 2020.

The Government has so far refused to hand over written proposals for its alternative to the backstop – the controversial contingency measure which would keep the UK closely aligned to Brussels’ rules in order to prevent a hard border with Ireland.

Mr Rinne told reporters that he and Mr Macron “agreed that it is now time for Boris Johnson to produce his own proposals in writing – if they exist”.

“If no proposals are received by the end of September, then it’s over.”

Mr Barclay, speaking during a visit to Spain, said: “A rigid approach now at this point is no way to progress a deal and 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 suggested that it was now for the European Commission to shift its stance.

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France’s President Emmanuel Macron and Prime Minister of Finland Antti Rinne at the Elysee Palace (Thibault Camus/AP)

He added: “We are committed to carving out a landing zone and we stand ready to share relevant texts. But it must be in the spirit of negotiation with flexibility and with a negotiating partner that itself is willing to compromise.”

Mr Barclay also suggested that the EU’s call for a legally operational alternative to the backstop to be ready on Brexit day was setting the bar too high.

“The alternative to the backstop is not necessary until the end of the implementation period which is December 2020,” he said.

“Indeed this will be shaped by the future relationship which is still to be determined.

“In short, why risk crystallising an undesirable result this November when both sides can work together until December 2020.”

He warned: “The EU risks continuing to insist on a test that the UK cannot meet and that the UK Parliament has rejected three times.”

Mr Barclay said failing to leave the European Union on October 31 was “not an option for this Government” but was challenged over how Mr Johnson’s administration would comply with the law aimed at preventing a no-deal Brexit.

The Cabinet minister said “of course we will abide by the law” but he added “we will look at it closely and test exactly where we are” – the latest sign that the Government is examining ways around its measures.

Mr Barclay said he was “surprised” that the EU claimed it was prepared for a no-deal Brexit – pointing to the potential impact on food and medicine supplies to Ireland if there are tailbacks at Calais.

“Two-thirds of Irish medicines come through Great Britain. 40% of its exports go through Dover,” he said.

“Its supermarkets are supplied from distribution centres in the Midlands yet this is presented as solely a UK challenge.

“It’s a mutual challenge because if indeed there were two-and-a-days of delays at Calais then the impact of that would not solely be felt within the UK, it would be felt in Ireland and indeed in businesses here in Spain.”