Wrekin MP Mark Pritchard today led calls for a full investigation into how the Prince of Wales and the Duchess of Cornwall came to be embroiled in the protest which escalated in the wake of a Commons vote to treble tuition fees.

The Tory said the incident – which saw the royals’ car attacked by rampaging protestors – could not be left to an internal Scotland Yard probe.

The royal security breach has raised questions about the way police handled the demonstration.

The couple were visibly shaken but unharmed after protesters smashed a window. Paint was also thrown at their armoured limousine as they were being driven to the Royal Variety Performance through central London last night.

A spokesman for the Prince of Wales and Duchess of Cornwall said the royal couple “totally understand the difficulties which the police face” and are “always very grateful to the police” for the job they do.”

Prime Minister David Cameron said the “mob” must be arrested and punished.

He admitted he was “very concerned” about the “very regrettable” lapse in royal security – and said that Metropolitan Police Commissioner Sir Paul Stephenson would report on it.

But Mr Pritchard insisted there should be an independent inquiry. He said: “This was an incident that was so very serious – and could have been even more serious — that it should not be left to an internal Metropolitan Police inquiry. There needs to be an independent inquiry.”

Ludlow Tory MP Philip Dunne added: “It does seem surprising they took a route blocked by students, which I think the police need to explain.”

Sir Paul said the armed officers protecting the royals showed “enormous restraint”.

Some 34 people were arrested for a range of offences. Benches were set alight in Parliament Square and the statue of Winston Churchill vandalised. A 20-year-old student was left uncons-cious with bleeding on the brain after an officer allegedly hit him on the head with a truncheon.