The biggest obstacle to a live televised debate between John Major and Tony Blair - the threat of a lawsuit from the Liberal Democrats - looks certain to be overcome.

It appears there are at least two ways round what the Labour leader terms "the problem of Paddy". The option most acceptable to the Lib Dems would be to have their leader debate with his Labour and Conservative counterparts before they go head-to-head against each other. But, if an agreement cannot be reached on a series of three debates, it is not entirely inconceivable that the BBC will steam ahead and simply stage a Major-Blair duel.

Mr Major endeavoured to display his belief in fairness yesterday when, announcing the date of the election on the steps of Downing Street, he stated: "I have some sympathy for Mr Ashdown's position. I am sure the broadcasters may find some way to involve him."

The Prime Minister swiftly added that he thought the principal clash should be between him and Mr Blair and that "a responsible, long debate dealing in detail ... will enhance the democratic process, not damage it."

The Labour leader said he was prepared to go head-to-head with his Liberal Democrats counterpart if this were required to get a separate crack at Mr Major. "I can't believe there's not a way round the Paddy problem," he said. Later, Labour's deputy leader, John Prescott, said his party had been calling for the televised debate for some time and they "didn't mind at all" if the Liberal Democrats were included.

But he told BBC Radio 4's World at One programme that it was important that there was audience participation.

Mr Ashdown said he would welcome the opportunity of taking part in a televised debate. "It is absolutely vital people get to hear the different options on offer," he said. More colourfully, the Lib Dems' campaign chairman, Lord Holme, said that granting Mr Ashdown only a "walk on part" would be like an edition of Blind Date in which two of the participants got to talk to the girl and the third only got to talk to Cilla Black.

The Liberal Democrats have been threatening to mount a legal challenge against the broadcasters if they don't stage a three-way debate or series of debates involving their leader. They would have a strong case against ITV, which has a statutory duty to be impartial under the terms of the Broadcasting Act of 1990.

But the BBC is not shackled to the same extent. It is governed only by a series of agreements in its charter which are open to challenge and are not set down in law.

Geoffrey Robertson QC, an expert on media law, said yesterday that the BBC had to decide if it would be in the public interest to hold a Major- Blair debate, and how it would ensure fairness. In his opinion, this might be achieved by letting the other party leaders comment, perhaps 30 minutes afterwards.