The Department of Health and the Prison Service appeared to be at odds last night over a needle-cleansing programme designed to protect prisoners from blood-borne infections such as HIV and hepatitis.

From April 1, inmates will be given disinfecting tablets similar to those used for sterilising babies' bottles. But health department officials said last night that cleansing tablets were not the best way to protect against the transmission of diseases.

"I don't think we would encourage this as being as effective as the issuing of sterile needles," a spokesman said. "We don't recommend it. We regard the needle exchange programmes in place throughout the whole of the [health] system as the most effective way of reducing blood-borne diseases."

A disinfecting scheme was tried in 1995, but was later withdrawn for safety reasons.

Doctors and drug-user support groups have also challenged the move, saying a needle exchange scheme would be safer and more effective.

Critics claim ministers fear that the introduction of a needle exchange scheme would be a tacit admission of the scale of the drug problem in prisons.

"There is no foolproof way of cleaning injection equipment - it is easy to get the cleaning process wrong," said Michael Linnell of Lifeline, a drug support agency.

"You could be encouraging people to share because they think the equipment has been cleaned. That increases the risk of spreading blood-borne viruses."

A Prison Service spokesman said the cleansing tablets were being introduced rather than needle exchange schemes because they allowed drug users to keep their equipment clean in a less ostentatious way.

He added: "These tablets can be used to clean a variety of things. Drug use is obviously against prison rules and having people queuing for a needle exchange programme could have ramifications for good order within prisons."

The Guardian has obtained a copy of Prison Service instructions on the scheme issued to governors, including those in private jails. It says the policy aims to combat "the spread of HIV and other blood-borne viruses such as hepatitis, [which] are readily spread when drug users share contaminated injecting equipment".

It points out that "similar arrangements have worked well in Scottish prisons since 1993".

The Prison Service says the scheme was approved by the London School of Hygiene and Tropical Medicine, which was asked to design a strategy for the reintroduction of disinfecting tablets at all penal establishments.

The school believes that a pilot scheme at 11 prisons in 1998 and 1999 was successful, and that the scheme should operate in all prisons. The home secretary, David Blun kett, has accepted its advice.

Last night a spokesman for the Department of Health said it was not opposed to the cleansing scheme in prisons. "Whilst it is acknowledged in the community at large that needle exchange programmes are an effective method, there are drawbacks to similar schemes in institutional environments," it said.

But a GP who practises in an area with a high rate of heroin use said: "Disinfectant tablets may prevent the spread of some skin diseases, but are unlikely to combat blood-borne viruses effectively."

The use of heroin and other class A drugs has become a serious issue in prisons. Some argue that the increase in use of such drugs coincided with the introduction of mandatory drug tests in the early 1990s.

Prisoners are aware that opiates such as heroin are only detectable for up to 48 hours after consumption, whereas cannabis, which used to be many prisoners' preferred drug, is detectable for longer.