Image caption Police officers were warned not to take "heavy-handed action"

The Metropolitan Police believed it had a "cunning plan" to deal with last year's tuition fee protests, according to a briefing document seen by the BBC.

The Scotland Yard paper said police needed to respond "quickly and effectively" to outbreaks of disorder.

Its unnamed author said: "To do this, we have developed a cunning plan: the essence of which is flexibility."

But during the protests police could not stop a breakaway mob attacking a convoy carrying Prince Charles.

The paper which echoed the phrase used by the hapless Baldrick in the TV series Blackadder was called Students' Action 8/9th December 2010 and written by an unidentified senior officer.

It detailed the police's preparations and was circulated before the protests. It was obtained by the BBC under the Freedom of Information Act.

During the protests police were unable to stop a mob breaking away from the main demonstration in Westminster and attacking a convoy carrying Charles and the Duchess of Cornwall in the West End.

The incident was deeply embarrassing for the Met and prompted an internal investigation and an apology from the force's Commissioner, Sir Paul Stephenson.

Under another section of the document, headed "negative photo opportunities", police were advised not to draw attention to themselves when waiting around in police vans:

Avoid hasty actions or taking the bait - this will require nerve, discretion and discipline Met police briefing document Read the full document on our Open Secrets blog

"If drinking coffee or reading the paper when embussed (sic), please be discrete (sic)."

The briefing paper also said police vehicles, sometimes known as carriers, should be parked with the driver remaining inside or "out of harm's way" - a reference to what had happened two weeks earlier when officers left a police van in Whitehall where it was smashed up, daubed with graffiti and looted.

"Ideally we want to be able to use our carriers again in the future," the document said.

The first student demonstrations against tuition fees took place on 10 November 2010 when protesters stormed the office complex housing the headquarters of the Conservative Party.

Scotland Yard was criticised for the way it responded and admitted later that it had not been expecting violence.

Briefing documents drawn up beforehand confirmed this and showed that police officers would not initially have full protective clothing and equipment.

In a police "draft tactical plan", Chief Superintendent Andy McKechnie writes: "There is no intelligence to suggest the need for public order kit at this stage."

Further briefing notes suggest police believed there had been an increase in "militant activism" and that some students would try to "goad" officers into taking "heavy-handed action".

"Avoid hasty actions or taking the bait," the document said. "This will require nerve, discretion and discipline."