The government was accused tonight of giving itself draconian powers to clamp down on protests at the 2012 Olympics. Critics said the powers were so broad they would potentially give private contractors the right to forcibly enter people's homes and seize materials.

Opposition parties and civil liberties groups criticised the powers as top security officials announced plans concerned with keeping the games, to be held mostly in London, safe from terrorist attack and from "domestic extremists" and public order problems like disruptive protests.

The legislation is directed at curbing advertising near the Olympic venues. A government spokesperson said the laws, passed in 2006, were meant to stop "over-commercialisation" of the games.

But civil rights campaigners are worried about several clauses in the London Olympic Games and Games Act 2006. Section 19(4) could cover protest placards, they said, as it read: "The regulations may apply in respect of advertising of any kind including in particular – (a) advertising of a non-commercial nature, and (b) announcements or notices of any kind."

Section 22 allows a "constable or enforcement officer" to "enter land or premises" where they believe such an advert is being shown or produced. It allows for materials to be destroyed, and for the use of "reasonable force". The power to force entry requires a court warrant. Causing still further concern is a section granting the powers to an enforcement officer appointed by Olympic Delivery Authority.