Ulster Unionists and the DUP have accused each other of vote-splitting in marginal constituencies which could enable nationalists to get elected.
David Trimble said the Democratic Unionists were too concerned with their overall vote tally when they should be worried about unionist representation in the next parliament.
"I have to say that the strategy adopted by the DUP of trying to focus on totals of votes rather than totals of seats is essentially bogus, and for a Westminster election is intellectually dishonest - what matters is seats.
"The strategy adopted by the DUP has reduced the number of unionist seats from a potential 12 to 11, and could potentially reduce it further by splitting the vote in South Belfast."
However, the DUP's North Belfast candidate, Nigel Dodds, accused the UUP of failing to reach a pact over agreed candidates.
"The Ulster Unionist Party is more intent on self-preservation than ensuring unionism stays number one in Northern Ireland.
"Their recent pact proposals were clearly aimed at protecting themselves, and they even advocated unionists voting for the SDLP."
On comments made by the Rev Ian Paisley, Mr Trimble accused him of damaging the standing of unionists at Westminster.
Dr Paisley, forecasting sweeping gains for his party at the UUP's expense, said he believed Mr Trimble was headed for "the electric chair and the rope". Mr Trimble said this represented the "nasty face of politics".
Dr Paisley said yesterday he did not believe the IRA would ever leave the stage. He said of the IRA: "A leopard doesn't change its spots."
Meanwhile, the Electoral Office in Derry has said number of postal votes issued for the general election are at an all time high, prompting fears that the outcome of the May 5th poll in the Foyle constituency might well be decided by postal votes.
In a constituency where SDLP leader Mark Durkan and Sinn Féin candidate Mitchell McLaughlin are said to be running neck and neck, the number of postal votes approved for election day were confirmed last night as being 2,430, an increase of 122 per cent on the 2003 Assembly election and an increase of 77.5 per cent on last year's European election.
The Foyle constituency has an electorate of 69,207 and the number of postal votes issued and approved represents almost 3.5 per cent of the electorate.
"Of the total figure of 2,430, an incredible 1,680 are new issue. That new issue figure is more than the combined number of postal votes approved for the last two elections. It's just phenomenal," the spokesperson said.
Since its creation in 1983, Foyle has been represented by former SDLP leader John Hume, who in the 2001 general election had a majority of 11,500 over Sinn Féin.
However, in the 2003 Assembly election, Sinn Féin closed the gap to just 1,500 votes.