Uniform guidance for family gatherings at Christmas must be devised between all four nations of the UK, political leaders have been urged.

Boris Johnson, Nicola Sturgeon, Mark Drakeford and Arlene Foster were warned that their governments must “accept the inevitability” that people will travel over the festive period.

The call came in a letter from the Liberal Democrats in Scotland, Wales and England – together with the Alliance Party of Northern Ireland.

They said guidance cannot be made in isolation given the “interlinked” nature of life in the UK, and called for a “four nations summit” to agree a plan.

The letter states: “It therefore falls on you and your counterparts to work across governments to explore workable solutions that can enable travel to happen safely.

“To manage the implications for public health, we are urging you to hold a four nations summit to co-operate on students’ return, to agree uniform guidance on the number of people who can gather, and to explore how best to expand travel options to allow social distancing.”

It is signed by Lib Dem leader Sir Ed Davey, as well as his Scottish counterpart Willie Rennie, Welsh Lib Dem leader Jane Dodds and Alliance Party deputy leader Stephen Farry.

Sir Ed said: “No one country can manage this challenge in isolation. The fractured rules across the UK have already been incredibly difficult to piece together.

“We need a four nations summit to agree on one set of uniform guidance for Christmas that works for families across the UK. Ministers across Britain need to start work on it now.”

Despite the UK taking a near uniform approach to lockdown restrictions at the start of the coronavirus crisis in March, the picture across the country is now more fragmented.

In Scotland, First Minister Ms Sturgeon has said her Government is looking at phased term dates and possible testing of students, and issues of people returning home where there are vulnerable people.

Welsh First Minister Mr Drakeford has said the current “firebreak” restrictions should give a pathway to Christmas “without needing a period of this severity of restraint between now and then”.

In England, Downing Street has said it is the Government’s “ambition to ensure that people may celebrate Christmas as a family this year”.

Former senior judge Lord Sumption warned there were “serious social and mental health issues involved in keeping grandparents away from the Christmas table”.

He told BBC Radio 4’s Today programme: “Let’s be clear about what this involves. It involves leaving grandparents out of it in the great majority of cases, and that really raises questions which go well beyond public health and actually well beyond law.

“What choices you are prepared to make in order to lead to a life worth living is an intensely personal question. People know the risks and they must make their own choices as to what to do. There isn’t a single answer which can be dictated by ministers in Whitehall.

“I think that there are serious social and mental health issues involved in keeping grandparents away from the Christmas table, supposedly for their own protection, when they may actually prefer a better quality of life.”

Broadcaster and peer Baroness (Joan) Bakewell spoke about the “moral imperatives of caring and loving for each other”, adding: “It seems to me that many older people might be prepared to take the risk. How many Christmases have you got left in your life that you’re prepared to give up one just for the sake of perhaps living a little longer?

“I think it’s going to be a moral decision that families are going to have to take. You can’t legalise it, you can’t police it, so people are thrown on their own resources to work this out for themselves.”