The three historic houses owned by Historic House Hotels (HHH) have been donated to the National Trust to ensure their protection and conservation.

After 30 years of talks between HHH and the trust, Hartwell House near Aylesbury, Bodysgallen in North Wales and Middlethorpe Hall in York, have now been declared inalienable (unable to be sold), therefore protecting them from inappropriate development.

The properties will continue their role as country house hotels under the management of HHH. All profits will go to the Trust to provide long-term care for the houses.

HHH was established 30 years ago with the intention of providing a secure new use for country houses at risk, ultimately to become the property of The National Trust. In 1997 the National Trust accepted restrictive covenants over the three properties, as a half way step.

Dame Fiona Reynolds, director-general of the National Trust, said: "The trust's survival is highly dependent on gifts and legacies large and small. These properties will help our work and contribute importantly to the upkeep of houses, nature, coastline and landscapes."

Hartwell House, a Georgian and Jacobean Grade I-listed property, is situated in 90 acres of parkland. Now a 50-bedroom hotel, the building was once a home for the exiled King of France Louis XVIII and his court. Middlethorpe Hall was restored and converted into a hotel from its use as a nightclub in the 1980s.

Grade I-listed Bodygallen Hall was the first property to be restored by HHH and opened in 1982 and is situated on 220 acres of park and farmland with views overlooking Snowdonia.

All three hotels feature a health club and day spa including an indoor swimming pool, whirlpool spa bath, a steamroom, a sauna, a gym and a Club Room. The treatments provided use products from Anne Semonin, ESPA, CACI, Jessica and St. Tropez.

A spokesperson for HHH said: "It is envisaged that arrangements will be put in place in the future for the gardens and grounds to be open to visitors, and also for guided tours of the ground floor rooms of the houses to be offered." The houses and gardens are currently accessible to hotel guests.

"While there is a strong commitment to continuing the hotel use, the situation has been considered, and provision made in broad terms, for the safe future of the houses, if at some time in the distant future, hotel use were to become no longer possible or appropriate."