BBC Political correspondent Nick Robinson has emailed staff at BBC Scotland's Pacific Quay HQ to apologise for 'becoming the story'after hundreds of demonstrators protested outside the building against alleged bias on the part of the broadcaster.

The controversy erupted after Mr Robinson reported from a briefing held for foreign press corps by Alex Salmond at which the senior BBC reporter asked a question.

Although Mr Salmond appeared to answer the question at length, but only partially, in a later bulletin Mr Robinson included his question and added simply "he didn't answer".

In the email, which was sent to senior editors and then distributed to all news staff at Pacific Quay by BBC Scotland political editor Brian Taylor on Sunday, Mr Robinson does not admit culpability.

However he says he understands colleagues may have been annoyed.

"Apologies if you came to work past today's protest and wanted to curse me under your breath - or, indeed, out loud," he wrote.

"I know how many people have been working long and hard to provide the fair and balanced and informative reporting people expect from the BBC, so that the people of Scotland have the information they need to make up their minds before they vote on Thursday.

"I do not want to be the story as I am sure you don't. So I am looking forward to getting on with my job and working alongside you over the next few fascinating and vital days."

An insider at Pacific Quay told The Herald that the BBC was currently highly sensitive to claims that its coverage has been biased towards a pro-union perspective and while most feel that it has not, there have been concerns that some English-based network staff despatched to work in Scotland have 'lacked sensitivity' to some of the issues at the heart of the referendum debate.

Slogans and banners criticising the BBC have become a feature of some gatherings of Yes supporters.

In response to the demonstration at Pacific Quay on Sunday, which featured calls for Mr Robinson to be sacked, the National Union of Journalists issued a statement condemning "hostility to journalists doing their jobs" and calling for an end to personalised abuse of those covering the referendum campaign.