The reason behind the sweep was this week's incident in the House of Commons (lower chamber) in which two visitors threw large packages filled with a purple powder at Prime Minister Tony Blair and his senior ministers.
The powder was later determined to be a harmless flour mixture. And the protesters were champions of a relatively uncontroversial cause -- the right of divorced fathers to have access to their children.
But the incident spurred genuine panic, with some members of Parliament fearing the powder could have been anthrax or another potentially lethal substance. Michael Martin, the speaker of the house, ordered the immediate evacuation of the chamber.
British Home Secretary David Blunkett reacted by suspending all public access to Parliament. And that was just a start.
"There are clearly going to have to be other restrictions which will make life more difficult for MPs, their guests, and those peers from the House of Lords [upper chamber] in terms of access to the open area of the House of Commons. That's very, very regrettable, but it demonstrates -- I fear -- that we'll have to do that in order to be able to protect people in the future," Blunkett said.
On 20 May, Leader of the House Peter Hain announced that in addition, a detailed security review will be conducted by MI5 in order to update the way Parliament responds to such incidents in the future.
"There are some hard lessons that need to be learned about what happened yesterday, and there will be -- as I described -- recommendations coming from the security service, which we will be able to consider early next week, and I think it is very, very important that what has been an old-fashioned culture of security in the house, is modernized," Hain said.
A $900,000 security screen over the house's public gallery has been in place since Easter. But this did nothing to deter the two powder-propelling protesters, who were there as invited guests.
The member of the House of Lords who had invited the protesters has apologized. The protesters themselves have been charged with threatening behavior.
But the incident has sparked a debate that reaches far beyond apologies and security overhauls: Could it be that the West -- which is responding with increasing panic to such attacks -- is actually losing the war on terror? And are terrorists -- by prompting ever-larger amounts of time and money to be spent on security -- winning?
William Hopkinson is an analyst with the Royal Institute of International Affairs in London.
"Vast sums are put into security, and if one is not careful one's whole way of life is distorted by these people. This is a real problem that the terrorists will get a sort of victory, both in the consumption of resources -- the economic victory -- and the psychological victory, how people feel about things," Hopkinson said.
Hopkinson adds that Britain does not yet appear overly "detached from normality." But he says, the danger that terrorist fears will change the country's democratic traditions is a real one.
"The United Kingdom so far has not given them [terrorists] very much to laugh about -- life has not been radically altered, and the vast majority of people don't go around living their lives as if they are likely to be subject at any moment to a terrorist attack," Hopkinson said.
Philip White is an analyst with the Economist Intelligence Unit in London. He feels that the danger of the terrorists gaining ground is still limited to the government.
"I think that governments all over Europe are probably a little bit jittery about security. And they are probably a bit more jittery about security in London than anywhere else, given the UK's profile over the last 18 months in Iraq and so on," White said.
As for average citizens, White says people have factored the risk factor into their daily lives but have not seriously altered their daily routines: "Lots of people have simply decided that it is best to get on with their lives, rather than sort of succumb to panic and never leave their front doors. I think the moment the people stop leaving their front doors is the moment that terrorists have won."