The First Ministers of Scotland, Wales and Northern Ireland have urged David Cameron to delay plans for an EU referendum.

In a letter to the Prime Minister, Nicola Sturgeon, Carwyn Jones and Arlene Foster raised concerns that a June 2016 vote could interfere with government elections to be held across the UK on May 5.

The First Ministers said it would be "virtually impossible" for political parties to fight both campaigns at the same time.

An in-out referendum on EU membership could be held as early as June 23 under current plans.

The First Ministers wrote: "We think it essential that those casting their votes are fully informed of the arguments on EU membership.

"As you know, elections take place in Scotland, Wales and Northern Ireland on May 5.

"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.

"We believe it would be better for you to commit to deferring the EU referendum at least until later in the year."

At Prime Minister's questions on Wednesday, Mr Cameron said voters would be "perfectly capable" of dealing with two separate ballots.

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

He said former Scottish 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."