By Donna Bowater

The intruder, who was initially thought to be a protester, was a crew member filming for a new BBC Three comedy show, which “pokes fun at the establishment”. 

Wearing a black suit and bow tie, Heydon Prowse tried to present Mr Osborne with a spiral-bound book labelled “GCSE Maths Exercise Book”.

It is understood Prowse was allowed into the event after he provided a false name and claimed he was filming a current affairs show.

Mr Prowse is filming for the show with collaborator Jolyon Rubinstein.

BBC spokeswoman Kate Toft said: “It’s making a political point in a cheeky way. It’s a BBC Three show, which will come out later in the year and it’s a sort of topical satirical entertainment show, which pokes fun at the establishment.”

She added the working title of the programme was We Know Where You Live, and it would air in late summer or early autumn.

The stunt appeared to unsettle the Chancellor, who was with Lord Mayor Alderman David Wootton.

Bank of England governor Sir Mervyn King and his wife were walking behind Mr Osborne at the time of the incident, witnesses said.

Onlookers said the episode was filmed on a small documentary camera before the crew was bundled out.

A similar stunt earlier this month at the National Gallery was also claimed by BBC Three.

A crew member hung a copy of Constable’s The Hay Wain on the wall of room 35 in the gallery in Trafalgar Square.

At the time, a source told the Evening Standard: “That someone was able to hang it in room 35 reflects the cuts that have been made in warders.

“It is impossible for one person to cover multiple rooms as there are too many blind spots. The policy of doubling up rooms will eventually lead to something more serious.”

Prowse – who hit the headlines in 2009 after covertly filming Conservative politician Alan Duncan saying MPs had been “nationalised” – and Rubinstein became internet hits with their satirical work for Don’t Panic Online.

The Daily Torygraph