The men in tights fight reform of Westminster security

A power struggle at the Commons could lead to resignations over the glaring breaches in security which were exposed by fox-hunting supporters and a journalist who smuggled a dummy bomb into the Palace of Westminster.

A power struggle at the Commons could lead to resignations over the glaring breaches in security which were exposed by fox-hunting supporters and a journalist who smuggled a dummy bomb into the Palace of Westminster.

It came as Alun Michael, the minister who led the Government on the Bill to ban fox hunting, pulled out of a right-to-roam march tomorrow in the Forest of Bowland in the North-west because of police warnings that he could be attacked by pro-hunting campaigners.

The threat to security at the Palace of Westminster spilled over yesterday into a dispute over modernisation between Commons and Lords authorities, which are blocking proposed change, and senior ministers, who are warning that al-Qa'ida could assassinate politicians with suicide bombs unless security is quickly tightened. Those demanding change include David Blunkett, the Home Secretary; Peter Hain, the Leader of the House; Lady Amos, the Leader of the Lords; Hilary Armstrong, the Chief Whip, and Bob Ainsworth, the Deputy Chief Whip.

They are locked in the battle over the modernisation of security with traditionalists including Tory MPs, the Speaker, Michael Martin; Black Rod, Sir Michael Willcocks, who is in charge of security for the Lords; and the Serjeant-at-Arms, Michael Cummins, responsible for Commons security.

Mr Ainsworth is said by friends to be "furious'' after having plans for a shake-up of security at Westminster thrown out by the joint security committee which he chairs.

Mr Ainsworth is appalled at the rivalry between the Lords and Commons officials - dubbed "the men in tights", led by Black Rod and the Serjeant-at-Arms. "There is a huge turf war going on. It is getting very nasty and it could lead to resignations," said one minister.

The modernisers intend to use a secret MI5 report on security at Westminster to be delivered shortly to force the palace authorities to back down and accept change. It will call for a new joint head of security for the Commons and the Lords, and curbs on vehicles entering the Palace of Westminster. MPs' taxis are likely to be banned from entering the Palace Yard to stop suicide bombers.

Other measures will include requiring all MPs to wear passes, and a security cordon around the base of the clock tower of Big Ben, which MI5 fear could be toppled by a lorry bomb from the road by Westminster Bridge.

The Speaker's Office hit back last night by making it clear that the Sun journalist did go through security checks before being given a pass, and insisting that any decisions will be for the Commons, not the Government. An "open house'' in the Commons this weekend will go ahead.

There were calls last night for more security around MPs in their constituencies after masked pro-hunt campaigners terrorised an MP's family. Phil Sawford, MP for Kettering, said his wife woke up at 4am on Wednesday to find a man in a balaclava and an accomplice in a monkey mask threatening to dump 10 tons of manure on their front garden in his constituency in protest at Mr Sawford's support for a ban on hunting. The masked pair also threatened action at the home of Phil Hope, the MP for nearby Corby and a junior minister. "They were attempting to terrorise my family. It is disgraceful action by despicable cowards. I am writing to the Speaker to ask for more protection for MPs in their constituencies," Mr Sawford said.

Mr Hain denied he was trying to turn the Palace of Westminster into a fortress. He said a move from medievalism to modernity was required to meet 21st-century threats. He accused parliamentary authorities of failing to improve security despite being shown "extremely disturbing" evidence of a terrorist threat to MPs.