BBC political correspondent Nick Robinson 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, it has emerged.

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.

"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."

 The Scottish Police Federation has dismissed political and media claims of heightened referendum tensions.

Its chairman, Brian Docherty, responding to a series of newspaper headlines accusing Yes campaigners of bullying and intimidating their opponents, cautioned against "exaggerated rhetoric".