NORTHERN IRELAND's Democratic Unionists have ruled out any formal Westminster deal with the SNP.

The staunchly anti-independence party's deputy leader Nigel Dodds said any pact with Scottish nationalists would be "bad for Northern Ireland and bad for the United Kingdom as a whole".

Mr Dodds' remarks came amid feverish speculation about how the DUP, which is forecast to win half of Northern Ireland's 18 Westminster seats, would use its weight in a hung parliament.

DUP leaders have previously said that the price for their support of either Labour or Conservative-led coalitions would be £1bn in extra spending for Northern Ireland.

However, Mr Dodds' intervention suggested his party would not back a Labour government supported formally by the SNP, which has, in turn, ruled out backing the Tories.

Mr Dodds, speaking on television, said: "We certainly would not be party to any kind of coalition or formal arrangement even short of a coalition which would involve the SNP which are out to break up the United Kingdom, wielding enormous influence over Ed Miliband and a Labour government.

"That would be something I think that would be bad for Northern Ireland, bad for the UK as a whole, because ultimately the SNP are about breaking up the UK, not furthering the interests of the UK."

The DUP has grown in to the dominant unionist force in Northern Ireland since it was founded by the late Ian Paisley in the early 1970s.

Mr Paisley, when First Minister of Northern Ireland, found common cause with his then Scottish counterpart Alex Salmond.

But his party, which backs a referendum on EU membership, had always been seen as a more natural ally for the Conservatives - and possibly UKIP - than Labour and the SNP.

Mr Dodds said he would not "negotiate publicly" what the party's position would be in the event of a hung parliament.

The DUP currently has eight seats but is widely predicted to take a ninth. Sinn Fein is forecast to retain its five Westminster seats but the Republican party's MPs historically do not attend parliament.