First ministers in Belfast and Cardiff follow call by Nicola Sturgeon not to hold vote in June over fears it could distract from assembly elections

The first ministers of Northern Ireland and Wales have joined a call by theircounterpart in Scotland for the EU referendum not to be held in June.

Scotland’s Nicola Sturgeon has previously argued that holding a vote on the UK’s membership of the European Union in June would distract from elections for the devolved administrations due to be held at the beginning of May.

Carwyn Jones, the first minister of Wales, is preparing to sign a cross-party letter to the prime minister from members of the Welsh assembly saying that holding the two votes in quick succession would cause confusion.

The letter is expected to say: “The simultaneous existence of multiple party political campaigns and EU referendum campaigns would in itself pose practical and logistical difficulties, but the greater problem we anticipate is the potential for confusion as a diverse range of issues is presented to the electorate.

“This is not just a matter of respecting the integrity of the Welsh electoral debate, but of affording the EU referendum campaign the respect it deserves.”

The Times reports that the letter was expected to be sent this week but the Welsh Conservative leader, Andrew R T Davies, is being pressured not to sign it.

Arlene Foster, who replaced Peter Robinson as Northern Ireland’s first minister this month, said: “I am of course a little concerned that if the referendum comes too close to the Northern Ireland [assembly] elections then the two issues will become integrated. That’s not what we want.”

Speculation is mounting that No 10 has pencilled in Thursday 23 June as the favoured date for the referendum. Cameron hopes to complete his renegotiation of the terms of the UK’s membership at an EU summit in February.

June is the preferred month as it would come ahead of a possible summer migration crisis, which could stir Eurosceptic feeling. If the referendum cannot be held in June, it is thought that September could be a backup. Officials say approximately 16 weeks must pass between the conclusion of a deal between Britain and the other EU members and the referendum.

Speaking to the BBC on Sunday, Nicola Sturgeon said holding the referendum so soon after the Scottish elections would be “disrespectful” to her country. The Scottish first minister said that it might look “a bit selfish” to be concerned about the clash with the Scottish elections, but that there were elections in Wales, Northern Ireland and London too in May.

“I think to have a referendum campaign starting in parallel would be disrespectful to those important elections,” said Sturgeon.

The government on Tuesday published secondary legislation setting out how the Electoral Commission would organise the referendum, leaving it open for the vote to be held in June. It confirmed that the ballot paper would ask whether voters wanted to remain a member or leave the EU.