The £2m restoration of the 12th century Westminster Abbey Chapter House in central London, considered as the birthplace of parliament, has begun.

The house, which was home to the King's Great Council in 1257 and became a meeting place for the House of Commons in the 14th century, will undergo the most comprehensive restoration project since architect Sir George Gilbert Scott worked on it in 1859. English Heritage is leading the project in collaboration with Stow and Beale Conservation Architects.

The project will focus on repairs to the external walls, which have been weathered by city pollution, and the repairing of the mixed limestone and sandstone stone work. Gargoyles and the stained glass windows will also be carefully restore and the lead roof and gutters will be repaired. The project is expected to be completed in 2010. Contractor Nimbus Conservation and manager Thinc Projects are also involved in the project. S T Walker & Duckham were the pre-construction architects.

Tim Reeve, properties director for English Heritage, said: “The Chapter House is a building of international importance and sits at the heart not just of Westminster Abbey but of the Westminster World Heritage Site, one of the most visited places on earth. This programme of repairs is an investment in London’s unique heritage so that present and future generations can enjoy this jewel of English history, the cradle of its Parliamentary system.” Barry Stow of Stow and Beale Conservation Architects said: "The early Chapter House was reportedly 'finer than Salisbury'. In medieval times it was used as a place of government, as a meeting place for the House of Commons and subsequently as a document archive.

"We are delighted to have been selected to conserve Scott's work which, in contrast to so much Victorian restoration, has benefited the public face of the Abbey complex as well as preserving the fine 13th century interior. We look forward to working with the contractor and project team to carry out an exemplary conservation project over the next 18 months."