Camden Council has turned down a planning application for a £135m extension to the British Museum in London, UK.

The proposed development, designed by architects Rogers Stirk Harbour + Partners (RSHP), had secured the support of English Heritage but had angered a local conservation group, Bloomsbury Conservation Area Advisory Committee (BCAAC).

RSHP's plans included a new 1,000 sq m (10,760sq ft) building at the rear of the museum, replacing the former offices of the British Library on Montague Place, as well as a conservation centre to train museum conservators.

BCAAC lobbied actively against the expansion plans, claiming that the development would block daylight from the existing buildings and would diminish the museum's existing architectural delights - such as Sir Robert Smirke's arched library room and J.J. Burnet's King Edward II building.

Museum officials will now be forced to rethink the proposals for the museum, which were initially announced in 2007.

In a statement, Camden Council said that it had considered every aspect of the application.

"Camden Council's Development Control Committee turned down the British Museum's plans for the north-west development,” it said.

“The application was recommended for approval and had the support of English Heritage. However, after careful consideration the committee decided that the proposed benefits of the scheme did not outweigh their concerns about the design within its context.

"The Council will continue to respond to the concerns of the community and other interested parties looking to take this project forward."