The First Ministers of Scotland, Wales and Northern Ireland have called on David Cameron not to hold the EU referendum in June in a joint letter.

Nicola Sturgeon, Carwyn Jones and Arlene Foster advised the Prime Minister that running an EU referendum campaign during the Scottish, Welsh and Northern Irish elections 'risks confusing issues at a moment when clarity if required'.

They also told Mr Cameron that holding the referendum in June would make it 'virtually impossible' for political parties involved in these elections to work together on the EU referendum campaign.

However, Mr Cameron rejected the demand, committing to a gap of at least six weeks after the May 5 elections before holding the referendum - leaving open the possibility of a vote on June 23 or 30.

The letter, also signed by Northern Ireland's deputy first minister Martin McGuinness, said: "We believe that holding a referendum as early as June will mean that a significant part of the referendum campaign will necessarily run in parallel with those elections and risks confusing issues at a moment when clarity is required.

"Furthermore, it will be virtually impossible for the political parties in our respective territories to plan effectively for, and where appropriate work together on, the referendum campaign while our own elections are in progress.

"We believe that the European referendum is of vital importance to the future of the whole United Kingdom and the debate leading up to it should, therefore, be free of other campaigning distraction."

At Prime Minister's Questions, Mr Cameron insisted that voters would be "perfectly capable" of coping with two separate ballots.

He was urged to rule out a June referendum by the SNP's Westminster leader Angus Robertson.

Mr Cameron said: "There is no agreement, so no date has yet been fixed for the referendum."

He said former first minister Alex Salmond had called for a six week gap between the May contests and the referendum "and I can guarantee that won't happen".

The Prime Minister added: "I do respect the former first minister of Scotland who said six weeks was what was necessary.

"I also respect the electorates of England, Scotland, Wales and Northern Ireland on the basis that I think people are perfectly capable of making up their minds in a local election or in a Scottish parliamentary election, or in a Welsh assembly election and then, a period of some weeks afterwards, making up their mind all over again on the vital question of the European Union."

He told MPs: "This House has voted for a referendum. It would be pretty odd if, having voted for a referendum we then spend ages debating about not having one."

Mr Cameron later added further fuel to speculation of a June 23 referendum, telling MPs that if a deal is agreed at the February 18/19 summit, four months "would not be too short" a period before staging the vote.