David Davis, the Brexit secretary, has said he “could live with” a 21-month transition period as Britain leaves the EU. He made the concession, demanded by commission negotiators, with EU talks in Brussels a week away.

Davis told BBC Newsnight: “I’m not bothered too much about the question of whether it is Christmas 2020 or Easter 2021.” He said that getting a deal at next week’s council was “more important to me than a few months either way”.

Theresa May first proposed a transition, or implementation, period in her Florence speech in September last year. She said that she thought it should last “around two years”, but when they set out their negotiating guidelines in January, the commission’s negotiator, Michel Barnier, introduced a December 2020 deadline.

A shorter transition period avoids complexities over a continuing UK contribution to EU finances in return for access to the single market and the customs union, which continue during the transition period. The new EU accounting period, called the multiannual financial framework, ends at the end of 2020.

Q&A What is a customs union? Show Hide A customs union means that countries agree to apply no or very low tariffs to goods sold between them, and to collectively apply the same tariffs to imported goods from the rest of the world. International trade deals are then negotiated by the bloc as a whole. For the EU, this means deals are negotiated by by Brussels, although individual member state governments agree the mandate and approve the final deal. The EU has trade deals covering 69 countries, including Canada and South Korea, which the UK has been attempting to roll over into post-Brexit bilateral agreements. Proponents of an independent UK trade policy outside the EU customs union say Britain must forge its own deals if it is to take advantage of the world’s fastest-growing economies. However they have never explained why Germany manages to export more than three times the value in goods to China than Britain does, while also being in the EU customs union. Jennifer Rankin

There had been indications that the government was ready to make the concession – one of a series it has had to make to keep talks on track – in return for a joint committee that would oversee the transition period to ensure that both sides acted in good faith. It would also mean that Britain’s voice could be heard if regulations affecting trade changed during the period.

But it is clear that Davis, who has attracted criticism for apparently preferring to tour EU capitals rather than attend negotiating sessions in Brussels, is most anxious to get a deal in March so that negotiations on the the UK’s future relations with the EU can begin. There has been speculation that agreement could be delayed until the next council in June.

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A shorter, clearly defined transition will please the government’s diehard Brexiters who complained that the UK would be reduced to the status of a vassal state if it had to take all the EU’s rules and rule changes without having a voice.

It is also part of a pattern however, where the British side in the negotiations holds out for one course of action – not paying any outstanding contributions, for example, or demanding trade talks run in parallel with the negotiating the withdrawal agreement – only to give in at the last minute.

However, some members of the European parliament’s Brexit steering group called for a longer transition period. Philippe Lamberts, a group member, told a press conference this week that it should last until the next UK general election in 2022 “so that we can see what the outcome is”.