The number of documents that may have been contaminated with asbestos at Waltham Forest Town Hall amounts to 5,000 bags, it has emerged.

It was revealed earlier this month that a "substantial" number of records in the basement of the building in Forest Road, Walthamstow, had been sealed off to staff following concerns they could be a health risk.

The council later said it had not yet destroyed any paperwork and would copy "important" documents, including legal and financial records.

But an internal memo reportedly written by chief executive Martin Esom has now emerged suggesting that it is too expensive to copy all of the paperwork and that the authority does not know precisely what is in all the sealed bags.

The note also says that dust containing all three types of asbestos - crocidolite, amosite and chrysotile - were found in the basement before any building work began this January, and that the presence of the fibres has been known about since the 1980s.

The memo says it would cost £375 per day to electronically scan the documents.

It states: “Any potentially contaminated archived files were manually logged on an inventory and contained in contaminated waste bags...It should also be noted that the logs only contain the information recorded on the outside of the files and not a detailed index of the contents.

“To indicate the scale of the operation, we have approximately 5,000 bags filled with documents and to scan each one will prove very expensive.”

Campaigner Nick Tiratsoo, of Odessa Road in Leytonstone, has been trying to obtain copies of expenses forms for councillors standing in the 2010 elections since February.

He said: "These new admissions are quite extraordinary.

"It now turns out that at the beginning of the current year, dust and debris containing the most dangerous types of asbestos was found in the town hall basement, an area frequented by staff.

"Nor are the comments about archived files any more reassuring. A substantial number are reportedly contaminated, but the council is vague as to its response, admitting it has no real idea about exactly which documents are in jeopardy.”

In 2010 the authority was criticised following a Health and Safety Executive (HSE) report which said that asbestos in schools had not been properly monitored or managed.

UPDATE: On July 25 the council issued this statement: "As most people are aware and as the Health and Safety Executive states, as long as the asbestos is not damaged or located somewhere where it can be easily damaged does not pose a risk.

"We have, however, had the Town Hall basement monitored on a regular basis.

"As previously stated, staff are at extremely low risk of exposure as testing confirmed levels were well within Health and Safety Executive guidelines.

"The safety and well-being of our employees is paramount, and staff have been given full health and safety advice and advised to visit their GP if they have any further concerns."

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