The mayor of London, Boris Johnson, is today beginning legal action to remove the peace protesters camping in Parliament Square.

If successful, the move is likely to see the eviction of long-term ant-war demonstrator Brian Haw, who has been demonstrating on the square opposite the Houses of Parliament for the past nine years.

Haw first set up camp in June 2001 in a one-man protest against war and foreign policy – initially the sanctions against Iraq.

He said he had been inspired to take up his vigil after seeing images and information produced by anti-sanctions campaign the Mariam appeal.

The father of seven has been arrested many times – most recently last week – but has successfully resisted repeated legal attempts to remove him, conducted both by Tory-led Westminster council and the former Labour government.

The site has become more crowded with the arrival of environmental protesters, who set up tents five weeks ago.

Greater London authority (GLA) officers acting for the mayor began proceedings for trespass at the high court today.

"Parliament Square is a world heritage site and top tourist attraction that is visited by thousands of people and broadcast around the world each day," a City Hall spokeswoman said.

"The mayor respects the right to demonstrate. However, the scale and impact of the protest is now doing considerable damage to the square and preventing its peaceful use by other Londoners, including those who may wish to have an authorised protest."

Johnson first outlined his decision to apply to the high court to begin legal proceedings for trespass last Tuesday – the same day David Cameron's Conservative-Liberal Democrat coalition government announced plans to "restore rights to non-violent protest" as part of its 18-month legislative programme.

The Conservative mayor's move has been welcomed by Westminster councillors. Colin Barrow, the Westminster council leader, has accused the protesters of "hijacking" the square.