The initial appeal is obvious for anyone struggling to save enough for the deposit on a house.

In fact it sounds almost too good to be true: dig your foundations and then use the free clay and sandy gravel you have extracted to build your walls.

But as a four-day course on cob building was coming to its conclusion yesterday, there was a growing conviction among the diverse mix of students that the ancient construction skill could also represent a bright future for them.

Army engineer Kenny George, 32, who attended the course in Fleggburgh, near Great Yarmouth, with his wife Cat, 29, summed up the optimism of the novice builders.

'Anyone could have a go. If you built sandcastles when you were a child you can build a cob house,' he said.

The couple, who are currently based in north Germany with their four children, are preparing for life after the army and are negotiating the purchase of a building plot near Barnstaple, in north Devon, for �60,000.

Mrs George said: 'When we tell people what we are planning to do they generally smirk. But if people saw what sort of house they could have, a lot more would do it.'

'We will end up with a four-bedroom home instead of our present small flat in Peterborough and, what's more, it will be built far more solidly than most modern-day houses,' added her husband.

Identical twins Alice and Hebe Wilcock, 29, of Hastings, East Sussex, also see cob building as the solution to their housing problem.

Alice, a stained glass artist, said: 'We both currently live with our mother and step-father and we would love to build our own place.

'It is a very, natural, intuitive way of building and you save money for the future as well as the present because the insulation is so good you don't need central heating.'

Kate Edwards and Charlotte Eve became cob enthusiasts eight years ago and their picture postcard cottage on the edge of Filby Broad stands as a testament to its potential.

An extension built out of the sandy subsoil dug from their garden has doubled the size and value of their 17th century home.

And the garden itself, a haven for wildlife from swallowtail butterflies to bitterns, has become the unlikely setting for an international, internet-driven business teaching cob building.

Ms Eve, 33, said: 'This year has just gone mad. More than 450 people have come here on courses and Kate also goes out into schools to teach cob building.'

She said students had come from as far afield as Japan, Saudi Arabia and Canada and at least 50pc were intent on going on to build a cob house.

She said: 'In addition to the Georges and the Wilcock sisters our latest course has a complete cross-section of people on it, from a postman to a professional musician. Demand was so great we had to put on another course in September and only have six places left on that.'

On a four-day course, costing �400, Ms Edwards, 43, takes students through everything they need to know from what to look for in buying a plot to the range of construction techniques, from basic cob building to lime rendering and mud plastering.

An energy-saving method used in their own home involves using lime rendered and clay plastered straw bales on the north facing wall to retain heat.

She said: 'It really is easy to do and people can end up with an impressive home for the same price as a very small terrace in Norwich.'

For more information, visit www.edwardscobbuilding.com