The house was sold in October for pounds 850,000 to a buyer believed to be an Egyptian millionaire, after the National Trust failed in an attempt to buy it because it had insufficient funds.
An offer was then made by English Heritage and the National Trust Memorial Fund, which would have kept the house and its contents together, but this was rejected by the then Secretary of State for National Heritage, David Mellor. The contents, many of which had been in the house since the early 17th century, were sold at auction for pounds 1,348,297.
Now English Heritage wants to reclaim a series of restoration grants paid to the Colthursts from 1983 for essential external structural repairs. English Heritage rules say that such grants must be repaid if a property changes hands within 10 years. This is so that owners cannot cash in if the value of a property is increased by work paid for out of public funds.
The Colthursts' solicitor, Richard Turner, said they had spent double the amount they had received from English Heritage. He said: 'The Colthursts spent 20 years of their life on the house, and a lot of effort. They inherited something that cost them dear but have not got a lot to show for their guardianship.
'If English Heritage reclaims this money, it is hardly going to encourage owners of other historic houses to behave in a responsible way as the Colthursts have.'
Mr Colthurst, who has appealed directly to English Heritage's chairman, Jocelyn Stevens, said: 'We offered to give the house to the nation. English Heritage's civil-servant attitude has come as a kick in the teeth.'
The English Heritage officer in charge of the case, Oliver Pearcy, agreed that the body was allowed to exercise discretion in the reclaiming of grants, but added: 'In this instance, if we were to choose our right not to recover the grant, it would have to be referred to the Department of National Heritage and the Treasury.'
English Heritage's own government grant was cut by 2 per cent this year. Mr Pearcy said that although the grants were spent on structural work, the house was worth more than it would have been if the repairs had not been carried out. He said the grants had been generous because of the heritage value of the house with its contents. 'You cannot say that to reclaim pounds 220,000 doesn't still leave them with a considerable amount of money.'