A HOUSE beside the River Severn built of mud, straw, wood and stone could win Britain's most famous architectural award tomorrow.

Cobtun, Nicholas Worsley's home in Northwick, Worcester, was built to an ecologically-friendly blueprint and designed by John Christophers of Associated Architects in Birmingham.

Now it has been shortlisted for the Royal Institute of British Architects' Stirling Prize, the winner of which will be announced by Kevin McCloud, of Channel 4's Grand Designs tomorrow.

"I am greatly concerned about our use of the environment," said Mr Worsley.

"The building industry uses an unnecessary amount of energy. We transport materials around the world when we could get them locally, and we make hard bricks when timber and insulation materials are easily available."

Cobtun is insulated with ground-up newspaper. Its outer wall, a continuation of the garden wall, is made of cob - a mixture of clay, straw, grit and water - pitchforked and trampled into place by Kevin McCabe, who specialises in cob work.

"The wall feels as if it has risen out of the ground and is merging back into the ground. It is not very visible," said Mr Worsley.

"The design of the house was a response to the site. I was lucky to find a rural site, overlooking the plain of the River Severn, but within easy walking distance of the city centre."

The rest of the long, low house is built of oak and stone, with a south-facing wall largely of glass.

"The water is heated with solar tubes, which are very efficient. The house is so warm that I don't use any gas after the middle of April, through to winter.

"I have just turned it on and had to turn it off again," said Mr Worsley.

He said sustainable materials were being used more in housebuilding, but people were still nervous of departing from conventional design.

"It probably costs the same, in terms of costs per square metre," he said.

Cobtun has been shortlisted for the Mansel Medal, awarded to the best one-off house in Britain. The winner will be announced tomorrow on Channel Four at 7pm.

"I hope that everyone in Worcester will vote for it," said Mr Worsley.