Jasmine by Albert Moore is being sold by the Watts Gallery in Surrey

The Museums Association said items that were not on show or used for research could become "a burden".

It is telling its 1,500 members to give unused items to other museums or public institutions - but they could also be sold in exceptional circumstances.

It is a major change of policy for the organisation, which has banned selling objects for 30 years.

The Museums Association (MA), which represents most museums and galleries in the UK, believes too few items are on view to the public.

"Museums typically collect 1,000 times as many things as they get rid of," MA director Mark Taylor said. "Wonderful collections can become a burden unless they are cleared of unused objects."

Vanessa Trevelyan, convener of the MA's ethics committee, said the disposal of items was "not without risk".

The Triumph of Love by Sir Edward Burne-Jones is also being auctioned

"But it is preferable to transfer items to an alternative home where they will be treasured, rather than retain material that is not supporting a museum's research, display or interpretation functions," she said.

The MA wants members to review their collections routinely and believes many items not on display will still be needed by their owners for research purposes or their archives.

It hopes the policy will also lead to many other pieces going back on display. But the organisation expects no more than a handful of commercial sales every year.

Auction

The change has partly been prompted by the Watts Gallery in Surrey, which promotes the work of artists George Frederick Watts and Mary Watts.

The gallery is under financial pressure and wanted to sell two paintings, which are not part of its core collection, to secure its future.

The Triumph of Love by Sir Edward Burne-Jones and Jasmine by Albert Moore, estimated to be worth �1.4m, will be auctioned by Christie's.