One of the photographs in the display is of the opening of Acomb hostel in Northumberland in 1933.

GMT supported his brother Charles in his decision to give Wallington to the National Trust.

In 1929 he inherited, from a relative, Hallington Hall, which is eight miles from Wallington. The hall stayed in the family until 1964, two years after GMT’s death.

GMT was Regius Professor of History at Cambridge, and wrote history books which were accessible to the "ordinary" reader. His History of England, published in 1926, was a best seller, while his English Social History sold almost 400,000 copies.

GMT used his wealth on projects such as buying Housesteads farm on Hadrian’s Wall in Northumberland so that the adjacent fort and its surroundings would be safeguarded.

GMT and his wife Janet owned Robin Ghyll cottage – now with the National Trust – which overlooks the Langdales in the Lake District.

He bought five farms to protect the area from development.

The Langdales are where his ashes are buried alongside his wife and their son Theo, born in 1906 and who died in 1911. GMT was one of the negotiators who persuaded the Forestry Commission not to blanket the central Lake District with conifers.

"His ideas led to the formation of national parks," says George, whose daughter, BBC correspondent Laura Trevelyan, wrote a book on the family which was published in 2006.

GMT was also a man of action in more ways than one.

In the First World War he commanded the British Red Cross unit on the Italian-Austrian front and was presented with the silver medal for valour by the King of Italy.

The exhibition runs until September 5.