A little-known family home with a fascinating history and an art collection featuring 18th century masters has opened its doors to the public for a summer season of tours.

Southside House overlooks Wimbledon Common and was once the principal manor house in the area, using the Crooked Billet and Hand in Hand pubs as its outbuildings and stables.

It was taken over by the once wealthy cotton merchant Pennington Mellor family from Biarritz in the 1930s, who bought the manor to house its valuable art collection - featuring paintings by Anthony van Dyck and Joshua Reynolds.

Much of what visitors can see today is a legacy of Major Malcolm Munthe - a writer and philanthropist who devoted himself to the house after returning from the Second World War with post-traumatic stress disorder.

The celebrated major started giving tours of the house while he was still alive, but many of his stories - such as one of Lord Nelson's lover Emma Hamilton dressing up as Greek deities in a guess-who game in the music room - were proven to be unfounded after his death.

Wimbledon Times:

"The history that the major wrote of the house, that his ancestors came here in the seventeenth century, was a complete fantasy", says curator Richard Surman.

"This was just all part of his need to recreate his own history so that he could have a buffer between himself and the world."

The house is now presented as a "psychological portrait" of the major, who was so convinced his family and home was under threat from attack that he slept in the basement to keep watch.

It was only about eight years ago, when Mr Surman took over the running of the house, that the real story finally began to be told.

But this only makes it all the more interesting to visit, with resident artists and friends of the existing generation of the Pennington Mellor Munthe family on hand to give tours on Wednesday, Saturday, Sunday and Bank Holiday afternoons.

Unlike many historic houses, where visitors have to peer over cordons to look into rooms and are forbidden to touch anything, at Southside visitors are free to closely examine the grounds and eclectic art collection.

It is full of hidden treasures, and Mr Surman said they are constantly uncovering new objects - most recently an 18th century puppet theatre and maps from Norway marking the places where German ammunition trains were blown up by Major Munthe.

One of the most fascinating paintings is a portrait of Chevalier d'Eon de Beaumont, a French diplomat and spy who is believed to have dressed up as a woman to infiltrate the court of the Empress Elizabeth of Russia.

The tour leads visitors from the reception room featuring a rocking horse said to have once belonged to Lord Nelson, through a "portrait corridor" to the staircase leading up to the Prince of Wales room - a bedroom Major Munthe claimed was once used by Prince Frederick Louis (1707-51). 

Other curious rooms include a small chapel, a homely study and a powder room where 18th century wigs were once refreshed as wearers inserted their heads into a hole so a servant could powder them on the other side of the wall. 

Wimbledon Times:

The house is now run by the Pennington-Mellor-Munthe Charity Trust.

It can be booked for exclusive group tours and regularly hosts musicians for intimate concerts.

For more information about the house, and to book a tour, visit southside.com.