Plans for a major redevelopment of the British Museum have received a boost after the institution was handed a £25m donation by two trusts established by the Sainsbury family.

According to the BBC, the Linbury Trust - set up by Lord Sainsbury of Preston Candover - is to contribute £12.5m over the next three years, which will help fund a new World Conservation and Exhibition Centre. The Monument Trust - established by Lord Sainsbury's brother Simon - has donated a further £12.5m towards the £135m project, which was given the green light by Camden Council in December 2009.

Plans drawn up by architects Rogers Stirk Harbour + Partners, include sinking part of the proposed extension below ground to help resolve criticism that it would block views of the Grade I-listed Reading Room. A British Museum spokesperson told the BBC: "This is an incredibly important project for the British Museum and has been planned for a long time."