More than 2,500 historic buildings will open their doors to the public at this year's Heritage Open Days as visitors numbers are expected to an all-time high.

Run by the Civic Trust and English Heritage, the scheme is expected to attract around 800,000 visitors to such historic buildings as Carlisle Castle, Thetford Priory, the National Monuments Records Centre in Swindon and St Mawes Castle in Cornwall.

The aim is to reveal elements of our heritage that are not usually accessible or charge admission fees, said Bobbie Williams of English Heritage.

Heritage Open Days has been increasing in popularity since its inception eight years ago and has been extended this year from two to four days. The scheme runs from 7-10 September.