Wentworth Woodhouse gives up its secrets as trust launches new tours of rooms never seen by the public before

Yet according to the guide and historian who will lead a new tour exploring parts of the Grade I-listed mansion never seen by the public before, part of uncovering the house's secrets involves separating myth from fact.

Steelworker turned archivist David Allott is happy to dispel the romantic legends surrounding this most loved of country houses - five miles of passageways are more like 2,000ft by his calculations, and the loose definitions and differentiations between rooms and cupboards mean an exact count is difficult.

The Hidden Wentworth itinerary and an upcoming tour of the cellars both cover such virgin territory that even the guides themselves are still learning as they go along. David recounts the moment a visitor discovered a graffiti 'signature' on the wall of a nursery etched by her electrician grandfather in 1955 which he himself had never spotted, while staff are still speculating on the original use of an underground reservoir that they believe may have once been a plunge pool for bathing.

Hidden Wentworth encompasses rooms that were used by the Earls Fitzwilliam, later owners the Newbold family and the staff and students of Lady Mabel College of Physical Education at various times in the estate's history - and each has a story to tell despite the visible dry rot and general state of neglect. The tour route allows for anecdotes to be told, such as the 'confetti trails' laid to lead guests back to their beds through the maze of corridors.

A house inventory from 1782 and old maps from 1830 have enabled guides to identify who slept where - from the suite allocated to relative and regular guest Peregrine Wentworth to the 'boudoir' used by Lady Milton, wife of the heir to the title, and the nurseries for the 14 children of the sixth Earl. The Fitzwilliams had modern luxuries and conveniences well before time - basins remain in the rooms and freestanding baths can still be seen. The original pre-1850 light fittings remain, having been converted for oil, gas and electric lamps over the centuries.

In later years, the house became a sort of rambling girls' boarding school when the trainee PE teachers of Lady Mabel College moved in - the tour takes in their principal Miss Casson's private rooms and the dormitories for the students, complete with 1970s curtains, retro kitchenettes and spartan bathrooms.

"There are a lot of mysteries to Wentworth, and we often see things we never noticed before. There are an awful lof of myths to dispel too. There are no secret passageways that we know of, and the rumour that all of the house's records were burned is a complete fallacy - they're safe in Sheffield Archives, and the bonfire people saw all those years ago was just rubbish from the estate offices.

"Each room is a piece of the jigsaw. People donate things that they think might help us and we often get rumours cleared up by pre-1979 guests of the family," adds David, pointing to a recent donation - the pamphlet for an 1849 excursion from Manchester to the house which included a description of work to the floor of the Marble Saloon that was previously thought to have been completed a decade later.

"We have found a few interesting things - cigarette packets left behind by the Intelligence Corps during the war, and a marble fireplace that had been boarded up. There are still many more mysteries to be revealed, and we often believe information is correct until someone tells us something that alters it."

David even speculates that the reason the family abandoned Wentworth after World War Two - when they retreated to a series of private apartments and allowed the women's college to take over most of the staterooms, before selling up in the 1980s - may not align with the conventional theories.

"People think they left because of the death duties, their coal mines closing and the male line dying out. I think it might have been more to do with social change - after the wars it was much harder to get servants, and a house like this needs them. The open cast mining in the grounds (ordered by the government) must have been horrendous for them. Luck was against them - the sixth Earl had eight sons, but 40 years later the only males left were bachelors in their 50s."

The Hidden Wentworth tour runs once a week. Adults tickets are priced at £35 and children's tickets £17.50, with a 50 per cent discount fot National Trust members.

Visit https://wentworthwoodhouse.digitickets.co.uk for tour dates.