After the UK left the EU on January 31, both sides had until the end of 2020 to negotiate rules for after the split.
The biggest grouping in the European Parliament, as well as some UK MPs, have advised the Prime Minister not to insist on ending Britain’s compliance with EU single market rules on December 31, while the world deals with the Covid-19 strain.
However, Mr Johnson has been adamant that the deadline can still be met and argues it should be possible to negotiate a comprehensive free trade agreement by then.
The Prime Minister’s spokesman said the Government had no plan to change course on the negotiations, telling reporters on Monday: “The transition period ends on December 31 2020. This is enshrined in UK law.”
The centre-right European People’s Party (EPP) said the coronavirus epidemic further complicated what many in Brussels regard as an unrealistically tight timetable for securing a deal.
MEP Christophe Hansen, a negotiator on the parliament’s international trade committee, said: “Under these extraordinary circumstances, I cannot see how the UK Government would choose to expose itself to the double whammy of the coronavirus and the exit from the EU single market, which will inevitably add to the disruption, deal or no deal.
“I can only hope that common sense and substance will prevail over ideology. An extension of the transition period is the only responsible thing to do.”
The warning comes as the EU-UK joint committee set up to implement the Withdrawal Agreement was set to meet for the first time.
Because of the outbreak, the talks will take place by video conference, with the British side led by Cabinet Office minister Michael Gove and the EU by European Commission vice president Maros Sefcovic.
The EU’s chief negotiator Michel Barnier is reportedly continuing to convalesce after contracting the disease earlier this month.
German MEP David McAllister, who chairs the UK co-ordination group in the parliament, said now was the time for the UK to change tack over an extension to the transition.
“The coronavirus pandemic complicates the already very ambitious schedule,” he said.
“The EU has always been open to extending the transition period. The ball is now clearly in the British court.
“The United Kingdom would have to submit an official request. So far, the UK Government has constantly rejected such an option.
“Under the current circumstances, London should carefully re-examine a prolongation.”
The Prime Minister’s spokesman added: “We have shared legal texts and they are the subject of informal discussions between ourselves and the European Commission.
“They are conversations that are taking place via telephone as both sides analyse each other’s respective legal texts.
“We’d expect those types of conversations to be carrying on this week.”