The government's chief vet has told BBC News she has no idea how many people keep chickens in the UK, which could cause problems in a bird flu outbreak.
There are at least 250,000 smaller scale poultry owners in the country
The authorities would be reliant on the media to relay advice and information to hobby farmers, Debby Reynolds said.
The government is setting up a compulsory registration scheme for all farmers with more than 50 hens.
But according to industry estimates there are at least 250,000 smaller scale poultry owners in the country.
Debby Reynolds told the BBC the authorities had built up a database over the years of who was keeping chickens, but this was very fragmented.
"There may be tens of thousands of them, but at the moment we just don't know," she said.
She said the government wanted keepers of poultry "to behave responsibly... to operate basic hygiene precautions, to look for signs of ill health and to report those to their veterinary surgeon".
'Slow to learn'
Senior vets and farmers say they are very worried about what they call the government's lack of energy and commitment to achieving a more accurate estimate of the numbers.
One senior industry figure told BBC News: "We are slow to learn the lessons of foot-and-mouth."
National Farmers' Union president Tim Bennett told BBC News the situation was unacceptable.
If bird flu hit Britain, commercial farmers would be expected to take measures to prevent the virus spreading.
But the spread would not be contained unless the government were able to communicate with everyone who keeps poultry, Mr Bennett added.
"It is not just getting the right messages across; I am just as concerned about people getting the wrong messages.
"There is plenty of people, and plenty of tabloid newspapers, who would be quite happy to spread alarmist messages, which would not be helpful at all."
Bird flu expert Professor Hugh Pennington told BBC News the government should already be ensuring the right advice and information was reaching small-scale hen keepers "on a regular basis".
"It is very important for information to go out that 'if you have a sick bird, call in a vet'.
"The other issue that concerns me is birds being bought and sold - foot-and-mouth spread because animals were being moved about," Professor Pennington added.
A spokesman for the Department for Environment, Food and Rural Affairs said they were regularly meeting members of the poultry industry to keep them up to date.
The poultry register, compulsory for farmers with 50 or more birds, was launched in November, and was also open to those with less poultry.
The deadline to register is next month, by which time 80% of all poultry keepers in the country would be accounted for, the spokesman said.
Currently the scheme is receiving 200 calls a day, with 5,000 so far registered.
"The decision to use 50 was that we were advised by experts that flocks of 50 or more posed a significant risk, in the event of an outbreak of Avian influenza, to the spread of the disease," he said.