Property: When a family home is a national monument, the caretaker is crucial

Living as if to the manor born need not be the sole preserve of those whose lineage extends back many generations. Renting a beautiful property through the National Trust is an option for those who wish to live in graciously-appointed accommodation. But as Penny Jackson warns, central heating should not necessarily be expected.

Terracotta figures look down on the Christmas scene at Lacock Abbey. A log fire blazes, holly and ivy have been brought in from the grounds and the tree has been positioned into its Gothick surroundings. But, for Petronella Dittmer, it is not complete until the hall is filled with musicians and friends.

Every year she organises a weekend of concerts at the house in Wiltshire and it heralds the start of Christmas for the audience as much as it does for her. It is also the time when the house, owned by the National Trust, reverts to being a family home.

After months of visitors, when the tenants can never be sure who is around the next corner, she and her husband can relax in a home that feels their own - which indeed it is, since a forebear bought it in 1539 for pounds 783.

It was a great-aunt of her husband, Anthony Burnett-Brown, who gave it to the trust in 1944. The couple may not be alone in relishing time in their ancestral home - even for a matter of days - but the manner is unique, and more stylish than most.

"One of the biggest joys is to have the bedrooms filled and the house alive with people who are good fun," says Petronella Dittmer, as she prepares to pack it to the rooftops with guests.

"It is a high point of living here, and it would dreadful if we didn't have this event. The house lends itself to music."

Ms Dittmer, a violinist as well as a singer, brings the Kensington Gore Singers to the abbey. She herself receives acclaim for recitals around the world. "There is nothing like playing in the abbey, though," she says, "and I feel it is so important to invite professional musicians into these lovely houses."

The balance the National Trust has to achieve if its properties are not to turn into museums is a difficult one, especially where the donor family is still in residence.

"I look forward to Christmas more than I dare admit," adds Ms Dittmer. "The hall is our family sitting-room. We have two lovely chamber organs in the corners and chairs round the fireplace, and we do things in the way the family has traditionally always done them.

"This is the only time we are ever completely private. There is nobody you have to say `good morning' to. Because it is an abbey, not a stately home, we can't shut ourselves up in a wing."

The house itself is not that big, but along with other tenants of historic properties Petronella Dittmer knows how cold it can get. Heating is one of the problem areas for the National Trust during the winter months.

If they were to heat houses solely for the comfort of those living there, terrible damage would be done to the furniture, fabrics and paintings.

"We have to compromise," says Helen Lloyd, of the National Trust, who is in charge of preventive conservation care.

The relative humidity has to be kept between 50 and 65 per cent, whereas in most houses it would be at about 35 per cent. Dramatic changes in temperature create the most stress on organic materials.

The ideal is an open fire, which gently heats the house by turning the chimney into a giant storage heater.

So does that mean there are running battles between freezing tenants and the trust for control of the thermostat? Helen Lloyd is diplomatic.

"Some heating systems have let us down."

Tenants rarely do. They are carefully selected, and certainly those who are attracted to a property that is open to the public on a regular basis will be enthusiastic and knowledgeable about its history. The level of rent they pay reflects the state of the house and their obligations.

Generally, the trust is responsible for the structure of the building, and the tenant for its day-to-day running costs and decorations.

One requirement might well be that the property cannot be left unattended, so a winter free of visitors does not mean an escape to the sun. (This clause does not seem to have deterred the 200 applicants for the tenancy of Derwent Island House in Cumbria.)

Off-season, the trust and its tenants have a few months in which to clean a house from attic to basement. Light exposure also has to be monitored, and this is a major reason for closing during the winter, says Helen Lloyd. "If we were open all year we would exceed museum regulations about the exposure of light-sensitive materials."

Many houses, though, do open briefly at Christmas for carols and mince pies. It may be the stuff of Christmas cards but it is also a rare occasion for local people to get together in what was once the "big house".

One couple, who took on a run-down 15th-century timber-framed house in Kent, look back fondly on their Christmas memories.

"We would have a huge roaring fire in the banqueting hall which went up to the rafters. But we never got over how freezing it was in winter," says Carrie Weston. "When we moved into our new house we put on all the radiators, just for the hell of it."

Letting of National Trust houses is through regional offices. Information from 0181-315 1111. Tenants are wanted for North Lodge, a 19th-century, centrally heated house with a domed roof, near The Vyne Mansion, Hampshire (01372 453401), and The Chantry, a seven-bedroom, three-bathroom house on Clumber Park Estate, Nottinghamshire (01909 486411).

Lacock Abbey Recitals for 1998: 01249 730042