Water reed imported from eastern Europe is increasingly being used by thatchers after a succession of wet harvests has more than doubled the cost of traditional long straw and reduced its quality.
But English Heritage, the government conservation body for historic buildings, argues that the use of imported reed is changing the face of the English countryside.
At a seminar in London today its chairman Sir Jocelyn Stevens will call on ministers to require owners to seek planning consent before re-thatching a listed building, to place greater emphasis on using local materials and traditional styles. He will say that thatched buildings should not be re-roofed with imported water reed or in a different style.
Prince Charles will be the main speaker at the conference, at which English Heritage will present guidelines on the materials and style to be used when re-roofing listed thatched buildings.
The guidance was welcomed by Christopher White, chairman of the National Society of Master Thatchers, one of several organisations representing England's 500 thatching companies and 1,000 thatchers.