THERE'S no such thing as simply changing a light bulb in Wilton House.

"The ceiling of the Double Cube room is 30ft up.

"In the old days, we used to have to build a tower scaffold and it would take three or four men," explains estate electrician Dave Colgrave.

These days, a machine lifts Dave up to the ornate ceiling, but to avoid emergency replacements as bulbs blow, all the bulbs in Wilton's magnificent rooms are changed at regular intervals, whether they need to be or not.

Nor is replacing a fuse a routine exercise, as all the electrical controls are in the roof space directly above the rooms.

"There's limited space and only one access point," says Dave.

"You go onto the roof and drop down between the roof rafters.

"Round the edge of the rooms is a 2ft-wide catwalk, but you have to crawl round it on your hands and knees.

"There are lots of awkward spaces in the house gaps in the walls between rooms and under the floors but it's quite fascinating.

"Most people don't know they exist."

Dave has got to know them all in the 29 years he has been employed as the estate maintenance electrician.

The job started as a response to a request from Lord Pembroke's clerk of the works to rewire two cottages in Burcombe in 1979, and it snowballed from there.

Now Dave (59), who lives in Downton, looks after all the properties on the 14,000-acre Wilton estate, including the house itself, Wilton Garden Centre, the Pembroke Arms, the Michael Herbert Hall, one farm and numerous cottages.

Special events, like the classical music and firework extravaganza in the summer and the marriage of Lady Emma Herbert, which took place in December, require additional lights to illuminate the beautiful grounds and extra power for catering equipment.

Films such as Pride and Prejudice, which used the house as a location, also need Dave's knowledge and assistance to reproduce the period-feel of the property.

"All the picture lights have to come down film companies don't touch the fixtures and fittings and then I have to reinstate them after filming," he says.

"It does make extra work, but it's brilliant when they are filming and the house is flooded with people."

Handling priceless chandeliers in the house have generated lots of comments about Del Boy, Rodney and their disastrous encounter with an antique light fitting in TV's classic comedy Only Fools and Horses.

He has, he says, heard them all.

"We try and be a bit more professional," he smiles.

Not that it is all plain sailing.

"When the Queen visited, all the fire alarms went off and all hell broke loose.

"It caused chaos until I could isolate it and say it was a false alarm."

It is, Dave says, a job that has made him a lot of friends and enabled him to meet many interesting people.

"I am so lucky to be here I wouldn't change it for the world," he says warmly.

"The first time they took me into the Double Cube room, I was dumbfounded for two minutes it's not your two-bedroom cottage!

"But it still has the same effect on me now it still gives me a tingle and a buzz."