The invasion of the House of Commons chamber by pro-hunt campaigners is an unprecedented breach of security in modern times.
Mr Blair was hit by purple powder in May while speaking
There have been a number of breaches in recent years but not since Charles I have people actually made it to the despatch box where the prime minister of the day stands.
But at a time of increased security because of terrorist threat, and new measures brought in after purple powder was hurled at Tony Blair four months ago, this latest breach seems set to lead to a new era in how Parliament is policed.
From abseiling lesbians to arms export protesters, BBC News Online looks back at some of the more memorable occasions.
July 1970 CS gas canisters thrown into the Commons debating
chamber from the public gallery
July 1978 Manure thrown from the public gallery during a Scottish devolution debate
February 1988 Three lesbian demonstrators abseil into the Lords during a debate on Section 28 - which banned the "promotion" of homosexuality in schools
June 1996 A group of demonstrators throw leaflets into the Commons chamber
December 1996 A pair of young women in the Strangers' Gallery unfurl a banner protesting arms sales to Indonesia before being bundled out by attendants
February 2004 Anti-war campaigners heckled the prime minister during a debate on Iraq
May 2004 Tony Blair hit by a condom filled with purple flour thrown by campaigners from the pressure group Fathers 4 Justice
September 2004 Parliament has to be suspended after five protesters get into the Commons chamber while MPs debate whether to ban hunting with dogs.