Beauport Park country house hotel in East Sussex off an asking price of £4m.
Bannatynes previously bought adjacent land from the hotel to open a state-of-the-art health club in 2005 which offered complimentary membership to hotel guests.
The group - which operates more than 60 health clubs (some with spas), hotels in Darlington and Durham, and a bar in Newcastle - now intends to convert the three-star Georgian hotel into a destination health spa.
Beauport Park occupies a 38-acre site in St Leonards-On-Sea and is just three miles from the coastal resort of Hastings and the historic town of Battle.
It was built in 1719 for the former governor-general of Canada, General Sir James Murray, who named it after his summer residence in Quebec.
Along with 24 en-suite bedrooms, the hotel has residents' and bar lounges, a 60-seat fine dining restaurant and conservatory brasserie, two linked conference rooms to hold 36 boardroom-style and 70-theatre-style, and a spring/summer wedding marquee on the front lawn to hold another 120 guests.
The gardens contain croquet and putting lawns, an all-weather tennis court, an outdoor heated swimming pool, and a nine-hole pitch and putt golf course.
The Maidstone office of Christie + Co sold the freehold by share transfer on behalf of Ken Melsom and Stephen Bayes, who have owned the property since 1983.
By Angela Frewin