Armed guards patrolled Britain?s parliament yesterday as an inquiry began into how pro-hunting protesters caused one of the nation?s most embarrassing security breaches in years by breaking into the debating chamber.

The eight men used a forged letter to enter the landmark Victorian building and were then apparently helped by someone inside with a security pass. Five of them, dressed in T-shirts bearing Prime Minister Tony Blair?s face, gained access to the debating floor, prompting the bizarre sight of ceremonial parliamentary guards ? in black stockings and tailcoats ? hauling them away. In typical parliamentary pomp, one guard even had a sword. Police were holding the eight for questioning yesterday.

As security was tightened around the site in central London, questions were increasingly being asked as to why a handful of men in tights are still allowed to be the last line of defence for the nation?s leaders at a time of heightened terrorism threats.

?The sight of five fit young men being pursued around the Commons chamber by middle-aged officials in frock coats was hilarious,? wrote The Sun?s political editor Trevor Kavanagh.

?Yet there are alarming implications for the security of this nation. The protesters came within yards of the prime minister?s office. Had they been carrying explosives they could have carried out a Beslan-style atrocity.?One of the five who stormed the chamber was Otis Ferry, the son of British rock star Bryan Ferry and a hunter himself.

The break-in ? which halted debate on a controversial government move to outlaw fox hunting ? took place two days after a fathers? rights campaigner dressed as Batman scaled a balcony at Queen Elizabeth?s Buckingham Palace.

The House of Commons protest came as a virtual riot was developing outside parliament where thousands of pro-hunting protesters had gathered. A hard core skirmished with riot police and at least seventeen protesters and two officers were injured. But concern yesterday was focused squarely on the break-in, rather than the violence.