Cameron urged to defer vote on EU to avoid clashing with elections to Stormont in May
Arlene Foster and Martin McGuinness have united with the leaders of Scotland and Wales to urge David Cameron not to hold a European Union referendum in June.
The First and Deputy First Ministers, along with Nicola Sturgeon and Carwyn Jones, have warned that a June vote would mean the referendum campaign clashing with May elections to Stormont, Holyrood, and the Senedd.
The first ministers said a June vote "risks confusing issues at a moment clarity is required" and urged Mr Cameron to "commit to deferring the EU referendum at least until later in the year".
The Prime Minister rejected that, committing to a gap of at least six weeks after the May 5 elections before holding a referendum - leaving open the possibility of a vote on June 23 or 30.
In their letter, the leaders 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.
"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."
Yesterday, DUP MEP Diane Dodds told the European Parliament that Mr Cameron's negotiations were "little more than a choreographed talks process, a faux battle, a smoke-and-mirrors charade that has resulted in little more than the status quo, a failure by our Prime Minister to stand up for our United Kingdom".
Meanwhile, an academic has said Brexit could have a "huge impact" on large firms' plans to establish bases in Northern Ireland once corporation tax is cut.
In the short term it would create added complexity, and could slow investment in the first couple of years, said Professor Neil Gibson, director of the Economic Policy Centre at the Ulster University.
He gave evidence to the Northern Ireland Affairs Committee of MPs at Westminster which is investigating the impact of any UK exit from the EU on Northern Ireland.
Mr Gibson said: "An exit vote would weigh on traders' considerations in the short term, I would not underplay the impact on Northern Ireland, having made its biggest policy choice ... in the first two years not much is happening.
"In the short run just the particular timing of that would have different implications. It would be a factor in those firms' decisions."
As part of last year's Fresh Start political deal, the date for a tariff reduction in the business levy, to 12.5%, will be April 2018, matching the Republic of Ireland in an effort to compete for investment. Currently the rate is 20%.
Advocates of a lower rate of tax on business profits in Northern Ireland point to a potentially transformative impact on a local economy that shares a land border with a jurisdiction - Ireland - where the tax is only 12.5%.
Business leaders envisage tens of thousands of new jobs and greater prosperity. But critics claim reducing the local rate so significantly from the UK's would damage public spending, as it would see the Treasury cut an estimated £300m off the Executive's annual funding from the rest of the UK to offset the loss in revenue. It could also help encourage businesses in the UK to relocate.