ALEX Salmond and Alistair Darling are likely to clash in only one more referendum TV debate in front of a live audience, it has emerged.

The First Minister and the chairman of the Better Together campaign have agreed in principle to meet in a BBC audience debate in Glasgow on August 25, but are not expected to do others.

Darling said this weekend that he hoped the confrontation would be broadcast across the UK on BBC One, rather than just on a Scotland-only channel and the internet, as happened with the inaugural STV debate last Tuesday.

"I would like to see it on whatever gets the widest circulation, but I'm not the broadcaster," he said.

Although Channel 4 and Sky have also asked the pair to debate, nothing has yet been agreed.

And if those debates do go ahead, the format is expected to be a studio with questions from a presenter, rather than an audience event.

Salmond and Darling have also agreed to an online debate for the influential Mumsnet website, although no date has yet been set.

Embarrassingly for BBC Scotland, it has also emerged that Salmond and Darling will not meet in what the broadcaster had promoted as "the biggest debate the country has ever seen". It is understood BBC chiefs spent £360,000 booking The SSE Hydro arena in Glasgow for the mid-September event without first asking the Yes and No camps who would be available for it.

The plan is to bus 12,000 first-time voters, a mix of 16 and 17-year-olds from every secondary in Scotland, to give them the chance to grill politicians.

But Better Together later ruled out Darling's appearance in any debate after August 25, as this is when postal ballots are issued, and up to one-quarter of Scots are expected to vote.

With the polls still showing No ahead, it is also to Better Together's tactical advantage to keep Darling away from a late scrap with Salmond in case he comes off badly in it.

It means the BBC One Hydro debate is likely to feature a panel of lower-profile politicians rather than the two key performers.

"STV have had a better referendum campaign than the BBC so far," said a senior SNP source.

The STV debate attracted 1.7 million viewers.

A BBC source said the broadcaster hoped its debate with Darling and Salmond would attract more viewers.