Ulster Unionist leader Mike Nesbitt has given a clear signal that his party will call on people in Northern Ireland to vote for the United Kingdom to remain in the European Union.

Sinn Féin, the SDLP and the Alliance Party have already said they will oppose a British exit, but the Democratic Unionist Party and the Ulster Unionist Party have not yet taken an official position.

Speaking at a conference in Dundalk on Friday, Mr Nesbitt said his party was "reserving its position" until the completion of the talks in Brussels but he warned about the potential dangers to Northern Ireland of a British withdrawal from the EU. He pointed to the significant funding the North received through farm payments, structural funds and money for peace-related projects. Peace funding has amounted to more than £2 billion since 1994.

He said a vote to leave could pose an "existential threat" to the UK as, in the event that a majority of voters in Scotland were in favour of staying in, it would probably trigger another independence referendum in Scotland. "As I see it, as a unionist, Brexit is about uncertainty," he said at the event, organised by the Centre for Cross-Border Studies.

Mr Nesbitt said Northern Ireland, the UK and the EU needed certainty and security. “All things being equal, I would hope to recommend that we stay in,” he said.

Ivor Ferguson, deputy president of the Ulster Farmers' Union, an organisation whose position on Brexit could have a significant influence on the referendum result in Northern Ireland, said it would take an official stance once the campaign began. However, he spoke at length about the potential dangers of leaving the EU. "From my point of view, it's a step into the unknown, a step into the darkness," he said.

The EU provides Northern Irish farmers with hundreds of millions of pounds each year while giving them access to foreign labour and a market of 500 million people. Without European money, Mr Ferguson said, food prices would increase by at least 30 per cent

Nigel Smyth, director of the Confederation of British Industry in Northern Ireland, told the conference that a study carried out by the organisation found 80 per cent of its members wanted the UK to remain in a reformed EU. He said Northern Ireland was heavily dependent on trade with the EU, with 57 per cent of its exports sold into the union. "Ireland is our largest export market, and a return to border customs controls would be harmful," he said.

June 23rd has been mooted a referendum day, but politicians in Northern Ireland, Scotland and Wales are pressing for a date later than in the year because they believe campaigning for a June referendum would cut across their proposed elections. The scheduled date for elections to the Northern Ireland and Welsh assemblies and the Scottish parliament is May 5th. Like the Scottish National Party, the Welsh nationalists of Plaid Cymru will be campaigning against a withdrawal. Jill Evans, a Plaid MEP, said it believed Wales's "natural home" was in Europe and would be "campaigning hard" to keep the UK in.

The Scottish Council for Development and Industry, which stayed neutral in the independence referendum, will actively campaign against a Brexit in the referendum. Ross Martin, the council's chief executive, said a vote to leave would have dramatic effects on the Scottish economy and put another independence referendum on the agenda. "The stakes could not be higher. What is to play for could not be more serious," he said. "The financial stakes are enormous. The social stakes are ever larger."

Edgar Morgenroth of the Economic and Social Research Institute said EU membership was a key factor in attracting foreign direct investment to the UK and that membership was shown to increase trade by 20 per cent compared to a bilateral agreement with the EU. "While a Brexit may make some people in the UK feel better, it is very likely to make everyone poorer," he said.