Thousands of homeowners have been warned that 10-year warranties supplied with their conservatories are likely to be invalid after the company that gave them went bust.

Midlothian-based Penicuik Windows & Conservatories was put up for sale by its joint receivers, BDO Stoy Hayward, last week. But The Herald has learned that the warranties it had previously given were "in-house" and not underwritten by an external insurer, meaning they would be invalid if any claim were to be made for faulty or damaged goods.

James Stephen, a partner in BDO Stoy Hayward, confirmed that the PWC warranties were supplied by the company and were unsecured.

"It may be that any prospective purchaser may look to assist as a matter of goodwill but that will be uncertain until the business is sold," he said.

BDO Stoy Hayward are asking customers with outstanding claims under warranties to make contact .

Mr Stephen said he did not have a figure for how many people were affected by the warranties.

"It is a 10-year warranty so it could go back some considerable time. Not every conservatory had issues and we would hope the vast majority would be OK," he said.

"The company is still trading so may look at potential assistance claims unsecured against the company.

"But any further work that has had to be done will have to be paid for. It is a regrettable situation."

The conservatory firm was forced to cull 59 of its 111 staff after it went into receivership. The company, which started as a family firm in 1975, made trading losses totalling £4.1m over the two years of 2004 and 2005 and owed £13m to creditors two years ago.

The firm was bought in 1998 by Andrew Steel, nephew of Lord Steel. He sold it three years later.

There are 13 parties interested in buying PWC, which would enable it to complete the £2.1m of existing orders stretching out until October, Mr Stephen said yesterday.

He said he was in the process of arranging site visits and holding further discussions with interested parties.

The warranties revelation provoked warnings from consumer watchdogs to check that guarantees are externally underwritten.

Peter McCarthy, senior lawyer at consumer lobby group Which? said: "If the warranty is issued by the company it is a contract between you and them. If they go out of business, there is no-one to sue if there is a problem."

Consumers should either try to buy externally underwritten warranties or buy goods using a credit card or finance - meaning they are covered for five years, he said.