Metropolitan police commissioner Sir Paul Stephenson faces mounting pressure after footage emerged showing an officer policing Thursday's student protests not wearing identification.

Following the G20 protests last year, during which Ian Tomlinson died after being pushed to the ground by a police officer not wearing ID, Stephenson said it was "absolutely unacceptable" for officers to cover or remove their shoulder tags bearing identification numbers. However, a video taken by one of the protesters at the London demonstration clearly shows an officer not displaying her ID.

Keith Vaz, chair of the home affairs select committee, said last night that he would be raising the issue with home secretary Theresa May on Tuesday at the select committee.

The footage emerged as reports said Stephenson had offered to resign in the wake of this week's protests, with the Met heavily criticised after a protester required brain surgery after allegedly being struck by a police baton. Protesters had also attacked a car carrying Prince Charles and the Duchess of Cornwall.

Today May confirmed there had been "contact" between Camilla and one of the protesters, reportedly involving the duchess being poked with a stick.

May, who insisted she had not considered resigning in the wake of the incidents, would not rule out using water cannon to control protesters in the future, insisting "it is right that we look across the board at all the options that are available".

Video footage showing the police officer not wearing identification was recorded by Chris Dowdeswell, a 27-year-old web developer from Gloucester, and posted on YouTube.

"We were in the kettle from the beginning on Parliament Square," Dowdeswell said.

"We were walking to the different police lines trying to find out what was going on, and someone told me we should film this one officer who was without her lapel numbers, without her identifying marks.

"When we questioned her at first, just before we started filming, she said: 'I'm a human being, not a fucking number'."

Dowdeswell, who runs the Brutal Cops website which aims to draw attention to police corruption and violence, said after he began filming the officer "looked awkward and embarrassed".

Shown the footage by the Guardian yesterday, a spokesman for the Met said the force would investigate why the officer was not wearing her identification tags.

"All officers were briefed before the demonstration that their shoulder numbers should remain visible at all times," he said.

"The demonstration command team is now aware of this footage. The Directorate of Professional Standards has been informed and steps are being taken to identify the officer in question, and obtain an explanation." The Met commissioner promised to take "proportionate" disciplinary action against officers who did not carry their ID badges.

Jenny Jones, a member of the London assembly and the Metropolitan police authority, said that officers not wearing identification numbers should be sacked: "Whatever Stephenson has done between G20 and now it hasn't sunk in on his officers, and therefore anybody actually found without their numbers on their shoulders should I think at this stage face dismissal. They've had lots of warnings."

Jones said: "I don't think [Stephenson] should resign over the protests, because I think that it could have happened to any officer." However, she added: "Moving on, its definitely going to be a case of whether or not he has the creative thinking to improve the situation, because it absolutely can't continue in this way, and the Met and the government have to be creative about the way they engage with students so that this doesn't happen again. I was very distressed at the demos that we've seen and I think that trust has broken down completely between students and the police and somehow they have to put it right."

The Sunday Times today reported that Stephenson had offered to resign after Prince Charles's Rolls Royce was attacked on Oxford Street, a source telling the newspaper the commissioner had "made it clear that if [the palace] thought he should resign, he would do so".

May is due to make a statement to MPs regarding the policing of Thursday's protests.

"The Metropolitan Police are looking into the details of that incident to find out exactly how it arose and of course they will be wanting to learn the lessons from that," she said.

Police were also criticised after a 20-year-old student, Alfie Meadows, 20, underwent a three-hour operation to treat bleeding on the brain after allegedly being hit on the head with a truncheon. Yesterday his mother, Susan Matthews, claimed that when Meadows was taken to Chelsea and Westminster hospital police objected to him being treated there as it was being used to treat injured officers. The Independent Police Complaints Commission has since launched an investigation. Meadows, a philosophy student at Middlesex University, is said to have made a good recovery so far, with his mother, Susan Matthews, saying "he's improving day by day".

Today police released images of 14 people they want to speak to following clashes during the demonstration, asking the public to help identify those pictured. The appeal came as Charlie Gilmour, son of Pink Floyd guitarist Dave, was arrested on suspicion of violent disorder and attempted criminal damage after he was photographed swinging from a flag attached to the Cenotaph on Whitehall on Thursday.

He is the 35th person to have been arrested following involvement in Thursday's protest. A total of 176 people have been arrested in the four protests so far.