A man who allegedly injured a police officer in an assault yards from the Commons chamber was released on bail today as fresh questions were asked about parliamentary security.

The alleged attacker, named today as Ian Thomas, founder of the publisher Sugar Media, had to be sprayed with CS gas after going "berserk" when an officer intervened to stop an argument with another reporter and a woman in a corridor.

The officer received treatment for a split lip after the attack.

With the start of the G20 only days away, questions remain as to how the alleged attacker and another colleague were able to carry their noisy argument to an area directly behind the Speaker's chair, only a few yards from one of the main doors leading to the Chamber.

Mr Thomas, 40, had been signed into Parliament as a visitor to attend a cocktail party for journalists hosted by the Conservative MP Eric Pickles in the Shadow Cabinet room. He was meant to have been escorted at all times to any other parts of the parliamentary estate. MPs taking part in a night-time debate reported that they could clearly hear the fracas.

A source said: "He had an argument which spilt into the corridor, at which point he was approached by a police officer who asked to see his ID and he completely lost it and went berserk. Clearly, he was not meant to have been in the corridor unescorted."

Kerry McCarthy, the Labour MP, wrote on Twitter that she heard the scuffle from inside the chamber. "Was in Chamber when Pickles' guest went on rampage. Much excitement, banging + shouting. Gillie Merron told us someone had set off CS gas," she said.

A Conservative Party spokesman confirmed that the men involved had been guests at Mr Pickles's party. "He was signed in in the normal way as a visitor, and of course no-one had any idea this was going to happen," the spokesman said.

In a statement tonight, the Metropolitan Police confirmed that a 40-year-old man had been arrested and then bailed until June 7.

"We understand two 'non-passholder' guests began arguing at a reception. Both men left the reception and subsequently entered a corridor in a private area of the House where they were stopped by a male police officer," the statement said.

"One of the men became aggressive and allegedly punched the officer in the face - he sustained a split/cut lip. CS Spray was used by the officer to restrain the 40-year-old man who was arrested on suspicion of assault. He was taken to a central London police station. The sittings of both Houses were not affected."

A spokesman for the Sergeant-at-Arms, responsible for security in the Commons, acknowledged that both men involved in the argument were "non-pass holders" but said that the office was awaiting further details before making another statement.

The incident marks the latest in a stream of security breaches at the House of Commons. Last year, campaigners of the climate action group Plane Stupid chained themselves to the roof of the Houses of Parliament to protest against the expansion of Heathrow airport.

It is thought that the protesters received the help of pass-holders in the Commons. In 2004, Hunt supporters stormed the chamber of the Commons while MPs were preparing to vote on the Hunting Bill. Eight demonstrators wearing pro-hunt T-shirts evaded all Parliament’s security checks to reach the floor of the House.

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