DAVID Cameron will watch the second televised independence debate between Alex Salmond and Alistair Darling.

No 10 sources said the Prime Minister was fully expected to tune in on August 25.

Mr Cameron was at the centre of a row earlier this month when Downing Street suggested he might not watch the first of the highly anticipated showdowns.

Just hours later, however, in an apparent U-turn, it was announced that he would be "catching up" with the debate while on holiday in Portugal.

But it is understood that technical problems with STV online player prevented him from watching any of the event live.

The next debate will be aired on BBC across the UK and to a global audience in over 100 countries through BBC World News.

Mr Cameron had been Mr Salmond's first choice of sparring partner in the debates.

But the Conservative leader held firm for months insisting that he would not take part and that it was correct that the pro-Union case was made by the Scottish leader of the campaign, Mr Darling.

Meanwhile, former Tory leadership contender David Davis has suggested losing the referendum could result in Mr Cameron having to resign.

Asked whether the Prime Minister would have to stand down, Mr Davis told the BBC: "That's his call. It will be particularly humiliating for him.

"It would be a humiliating point for any prime minister to have lost a part of the United Kingdom, no doubt about that."

John Curtice, professor of politics at Strathclyde University, said: "A Yes vote would destroy Cameron's place in the history books."

A Guardian/ICM poll conducted immediately after the STV debate last week indicated former chancellor Mr Darling had won the debate by 56 per cent to 44 per cent.

The BBC has said that audience questions will feature prominently in its programme.