Responding to comments by First Minister Peter Robinson in an interview with the News Letter on Monday, Sir Reg said that the DUP’s “attack dog approach to politics” was harming unionist unity.

But DUP deputy leader Nigel Dodds said that Sir Reg “chides others for attacking fellow-unionists then uses the entirety of his remarks to attack the DUP”.

“People can see through such a duplicitous approach.

“No matter how Reg Empey tries to spin, the facts are very simple: two seats can be won back for unionism at the next Westminster election, if there is an agreed unionist candidate.

“The DUP has offered Reg Empey the choice of either Fermanagh and South Tyrone or South Belfast. UCUNF can run in one seat and the DUP will fight the other. That way both seats can be returned to the unionist fold.

“Any time this simple proposition is put to him, Reg comes up with a whole series of reasons why it can’t happen.

“Instead of trying to justify a repetition of the mistakes of the past, where the arrogance of Trimble cost unionism two seats, Reg Empey should start focusing on a positive future for unionism.”

The DUP did not stand in Fermanagh and South Tyrone in 2001 but backed independent unionist Jim Dixon. Sinn Fein’s Michelle Gildernew took the seat by just a handful of votes from the UUP.

Sir Reg said that it was “misleading” to say that the DUP did not stand in the 2001 Fermanagh and South Tyrone Westminster election.

“The DUP supported an independent unionist candidate in that by-election – a candidate who said he would rather see the seat go to Sinn Fein than the Ulster Unionists.

“Mr Dixon won 65 per cent of the vote and we lost the seat by 57 votes – this is fact.

“Having sabotaged that Ulster Unionist seat, they repeated the process in 2005 by fielding a candidate in South Belfast, a seat which the UUP was defending.

“What political party is going to give away a seat it already holds?

“Nigel’s party split unionism in 1970 when it was formed on the basis of what it considered upholding traditional unionist policies.

“It appears to have abandoned those policies and is now quite happy to share power with Sinn Fein having promised their electorate not to do so.”