Mr Harley attacked the prospect of a ‘mansion tax’ on high value homes,
claiming that it would cause “unnecessary, long term and completely
unjustified damage”.

“Rational or sensible it isn’t,” he added.

The HHA represents 1500 privately-owned houses, castles and gardens across the
UK. In the past six years, the repair bill has risen by 50 per cent from
£260 million to £390 million. Occupiers of private historic homes cannot
recover VAT on repairs to crumbling architecture, leaking roofs or rotting
timbers.

As a result, owners must dream up novel ways of attracting visitors.

Dalemain, a Georgian-fronted house in Ullswater in the Lake District, recently
hosted a Hindu dog blessing while Eastnor Castle stages a thrice-yearly
mud-running competition in which competitors wade through water-filled pits.
Longleat, home to the Marquess of Bath, has introduced a Christmas ice rink.

Some owners have changed the face of their houses in order to draw in the
crowds. Patrick Boyle, the Earl of Glasgow, and his son, David, Viscount
Kelburn, alarmed some traditionalists by allowing Brazilian artists to cover
Kelburn Castle with graffiti.

Opening up houses for film and television locations can also be lucrative, as
Lord and Lady Carnarvon discovered when they allowed Highclere Castle to
become the setting for Downton Abbey.

However, Nick Way, director general of the HHA, said that lower profile houses
are in a more perilous situation.

He explained: “Around half of our members are dependent upon income from the
house itself. Some of them are nationally or internationally known
properties. But for smaller houses which open for 30 days or so a year,
meeting a £100,000 maintenance bill is difficult.

“It’s a competitive market and these smaller houses are up against Sunday
shopping, watching sport or going to the cinema when it comes to visitors,
so it is not easy.”

But it is not all doom and gloom. Historic houses welcomed 17.1 million
visitors last year and next year should see a boost in numbers thanks to the
tourist draws of the London 2012 Games and the Queen’s Diamond Jubilee.

Mr Harley said: “The Olympics allows us to focus interest on our heritage and
our houses. The Diamond Jubilee also resonates as a cause for celebration of
our heritage and our historic houses will continue working hard to ensure
this.”