A disastrous harvest of long-stemmed wheat straw for thatching has forced English Heritage to relax its guidelines on the use of traditional materials.

Britain has an estimated 60,000 thatched properties, of which about half are listed. Until now many planning authorities, backed by English Heritage, have insisted on the use of wheat straw for repairs and reroofing.

Alternatives such as water reed have not been permitted outside East Anglia where it is grown. Even triticale, a wheat-rye hybrid used successfully for more than 30 years, has not been permitted.

That was changed by last year's wet summer. Several of the few remaining growers of traditional long-stemmed wheat lost their entire crop and others managed to harvest only 30 to 40 per cent of what they expected.

The National Society of Master Thatchers (NSMT) says that the shortage of acceptable materials is now critical, with most of last year's stock used up.Supplies effectively ran out earlier this year and the price of thatching straw has more than doubled, from £600 to £1,500 a tonne.

Initially English Heritage advised owners to have their roofs patched but there is no longer enough straw to meet even that reduced demand. It is now urging planners to permit the use of triticale or thatch imported from eastern Europe, particularly Poland.

A spokesman said: “English Heritage is aware that the current straw shortage is causing problems to both home owners and thatchers. Our advice is always to respect local tradition and to use like-for-like material but in the current circumstance of a shortage of wheat straw we have advised local councils to consider triticale and imported wheat straw as possible alternatives.

“We also urge owners in the affected areas to think about repairs rather than recoating and to get independent advice about what really needs to be done. If recoating can be put off to a better year we would rather see that than the use of an inappropriate material. However, where recoating must be carried out we are content to see wheat straw brought in from overseas.”

Long-stemmed wheat straw was already in serious decline even before last summer's wet weather. Most cereal growers had switched to higher-yielding short-stemmed varieties that are less prone to wind and rain damage and easier to harvest.

The dramatic increase in the price of wheat this year means that even less is likely to be grown in future, creating seed shortages.

Roofs thatched with wheat straw typically need replacing every 15 to 20 years at a cost of £600 to £800 per 10 sq ft, the thatcher's traditional measure (about 1 square metre). Water reed, which is only permitted in areas where its use is traditional, can last 60 years.

Marjorie Sanders, a spokeswoman for NSMT, said: “Even if we have the very best harvest on the planet this year it will all go in a flash because we have so many properties waiting.

“The position following the very poor harvest this summer has now created a critical shortfall in the supply of cereal straw.”

Speaking in a Commons debate on Wednesday, Sir George Young, MP for Northwest Hampshire, said that the situation has become so bad that part of England's cultural heritage was now under threat from the very rules designed to safeguard it.

He said: “Replacement was evolutionary, reflecting the availability of materials and the thatcher's craft and style. In the past 20 years, intervention and control have begun to halt that evolutionary process.

“The balance must now be shifted away from conservationists, who have tried to freeze-frame the process, and back to owners and thatchers.”

Times recommends

• Prince Philip attacks big families
• Take a dip in Dubai-on-Thames
• Eco Worrier: How can I persuade my husband to use a push mower?