The letter went to the rates address of each of 1049 homes on record as having had Mr Fluffy asbestos insulation pumped into their roofs, so was received by home owners or managing real estate agents.

The letter came as a shock to some people, who did not receive or did not read the generically addressed letter sent in February which sparked the current crisis. Asbestos taskforce head Andrew Kefford said calls to the taskforce had spiked after the letter, up from fewer than 60 a day to near 100 a day. He could not say how many had discovered the Mr Fluffy status of their home for the first time, but said it was ''not a huge number''.

''Certainly I have spoken with and have had emails from a number of people for whom this was news, but tens, not hundreds,'' he said.

By Tuesday afternoon, 1673 people had registered with the taskforce. Of those, 1332 had identified themselves as a home owner, and the rest as real estate agents, tradespeople and the like. The taskforce is working through the registrations to match them to known Mr Fluffy homes.

The letter warns them that they must tell tenants in their houses, as well as potential buyers and tradespeople, as soon as possible.

''A number of families have asked if there is an obligation on them to inform other people about the presence of loose-fill asbestos in their home,'' Mr Kefford writes in the letter. ''The short answer to that question is yes.''

It also urges people to register with the taskforce as soon as possible, so they can access emergency assistance, including money for people forced out of their homes, asbestos assessments and rates relief.

Information from a former employee of Mr Fluffy, David Laughlan, suggested many more than 1000 homes might have contained the material, and estimates about the time of the clean-up program 20 years ago suggested as many as 8000 homes might have had the asbestos insulation pumped into their ceilings. Mr Laughlan said he did four or five homes a day in the six months he worked for the company, which operated for at least 11 years.

But Mr Kefford said the evidence suggested there was ''not a vast number'' of houses still containing the insulation and missed in the clean-up. The historic estimate of 8000 was based on a simple calculation of how many years the Mr Fluffy company operated for. But 20 years ago the government surveyed all 65,000 Canberra homes built before 1980 and found only the 1049, which were cleaned of the insulation but which might now face demolition after the material has been found still contaminating walls and other areas.

Since the clean-up, five houses have come to light that were missed in the survey. Mr Kefford said while he could not be ''absolutely definitive'', the low number suggested missed homes were not a big problem. He said there were a number of loose-fill insulation products, including Rockwool, Insulwool and cellulose fibre, which to an untrained eye looked similar to the Mr Fluffy asbestos. He stressed that while those products, and fibreglass-based insulation like Pink Batts, were ''not good'' to breathe in and should be used only with correct safety equipment, like any building material, they were of a different magnitude to asbestos. He urged anyone with a pre-1990 house to have an asbestos assessment before working on their house.

The government did not plan new surveys at the moment and was concentrating on the houses it knew of, he said.

The taskforce holds its second health forum on the issue on Sunday afternoon, at Hawker College in Murranji Street, Hawker.