Crazy impulse buys are as much a part of an annual holiday as overindulgence and sunburn.

But they are not usually quite as expensive as the "souvenir" bought by Ian Wood and Jo Stephens. They splashed out £85,000 on a whim.

Ian and Jo were, as he puts it, "having a wander through Andalucia" when they stumbled on a "for sale" sign and fell in love with a run-down farmhouse.

But rather than becoming their dream home, the 150-year-old house is to be part of a unique fund-raising project which will aid threatened wildlife in Sumatra.

After six months' hard labour, the once-derelict three-bedroom home in the hills behind the Costa del Sol is almost ready to rent out.

Rather than the profits going into the family coffers, the money will aid threatened orang-utans - and their human neighbours - in Indonesia.

Ian, one half of Sussex-based comedy duo The Invisible Men, and his wife Jo fell in love with orang-utans five years ago during a trekking holiday in the rain forests of Sumatra.

Ian, 39, from Westmeston, near Hassocks, said: "It was our third attempt at finding orang-utans - there are so few of them about.

"We hired a guide from the local village. It is a very poor area and our guide only had one shoe, even though we were walking eight hours a day through tropical rainforest.

"Eventually, while we were watching a group of monkeys, our guide came rushing over to say he had spotted some orang-utans.

"We went with him and found them up in the trees.

"We just sat there looking up at them. It was a surreal experience, almost like we were in the zoo with them.

"They are very unaggressive creatures. They broke off small sticks and threw them down to us. The eye contact we had with those peaceful creatures changed our lives."

Borneo and Sumatra, home to the world's last wild orang-utans, have lost 90 per cent of their populations during the past 100 years.

There are now about 30,000 of the creatures left and it is likely they will become extinct in the wild in as little as 20 years if the decline continues.

When they returned to England, Ian and Jo thought more and more about the plight of the animals and thought about setting up eco-tours to take other tourists to see them in their habitat.

Then a year ago the couple took an unexpected break in Spain and came across the farmhouse.

Ian said: "We rushed into it. It was a crazy impulse buy. But we knew if we didn't act there and then the idea would fade."

The pair splashed out more than £85,000 on the house and have since spent another £15,000 modernising it in a traditional style, installing a luxury bathroom and kitchen and building a swimming pool.

Ian said: "It is a different world from the hustle and bustle of the Costa Del Sol. It is a world of lakes, pine forests, bizarre rock formations, beautiful valleys and rolling hills where eagles soar on thermals.

"The idea of renting it is that people get to stay in a beautiful place and the money they pay is diverted to a cause that really needs help. Hence the name - A Good Place."

The WWF, the world's largest independent conservation organisation, works closely with Sumatrans, setting up sustainable projects which benefit animals and humans. They are excited by Ian and Jo's innovative fund-raising scheme and have become partners with them.

Ian said: "Normally when you come up with what you think is a good business idea, you keep it quiet in case other people copy it. In this case we and the WWF would be delighted if other people did the same thing for them and raised more money."

The couple hope to rent the house for up to 30 weeks a year and raise about £20,000.

Ian and Jo have done most of the work on the house themselves. Along the way they have also learnt Spanish, Malay and Indonesian, plus a good deal about the building trade.

Back home they are reasonably self-sufficient, allowing them to finance the Andalucian project.

Ian said: "We grow all our own fruit and vegetables and keep our needs down to a minimum so we are able to concentrate on the Spanish end of things."

The house will be completed and available for rent from next month. Although costs have still to be confirmed, prices for renting similar properties in the area are about £1,200 a week in peak season.

A web site is being developed. In the meantime, contact Ian or Jo on 01273 841536.