Two cocktail party guests of Eric Pickles, the Conservative party chairman, were last night sprayed with CS gas by a policeman in the House of Commons after fighting just yards from debating MPs.

One of the men was arrested and was being held at a police station in Central London. The two men, understood to be journalists, had been at a drinks party hosted in the Shadow Cabinet room.

After leaving at about 9pm, the men moved to another area of the Commons to continue an argument at the back of the Speaker’s Chair.

The chair is near one of the main entrances leading into the floor of the Commons and the row could be heard by MPs debating in the House. A policeman suffered a split lip as he tried to stop the row, which resulted in authorities spraying the men with CS gas, typically used to quell riots.

The gas was so strong that one policewoman reported that she had to leave because her eyes stung. Plain-clothes policemen were seen interviewing witnesses and security was increased.

It is believed that the men were signed into the House of Commons by an official passholder — someone who has been security vetted and who works within the Palace of Westminster.

Lord Mandelson, walking through central lobby, yards from where the incident had taken place, appeared shocked when told by The Times of the disturbance.

A Tory Party spokesman confirmed that the men had previously been guests of Mr Pickles.

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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