It is not quite as well-known as Stonehenge or parts of Hadrian's Wall, but Harmondsworth Barn in west London joins them as part of a national collection of historic sites under the guardianship of English Heritage.
The barn was described by the late poet laureate Sir John Betjeman as the "cathedral of Middlesex".
Arts correspondent Rebecca Jones speaks to Edward Impey, director of heritage protection at English Heritage, and Justine Bayley, secretary of Friends of Harmondsworth Barn.
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