LONDON–Come next year, smoking a joint in Britain might not seem so funny anymore.

Britain's home secretary says she plans to increase punishments for the use of marijuana, raising the maximum prison time for possession from two years to five.

The move by Jacqui Smith reverses the easing of penalties that took place under former Prime Minister Tony Blair. It also goes against the recommendation of the government's own advisory commission, which suggested that the law should remain unchanged.

But Smith says she wants to send a strong message to the public – particularly young Britons – that the drug is dangerous. She says evidence shows an increase of binge-smoking by young people – and the use of stronger varieties of cannabis, called skunk.

Smith says she wants to leave no doubt that the more powerful form of cannabis is illegal and harmful.

In order to take effect, the change must be ratified by both the House of Commons and House of Lords. The Home Office, Smith's ministry, says it expects the reclassification of marijuana to take effect in early 2009.

Cannabis had been downgraded from class B to class C – the lowest of Britain's three drugs classifications – in 2004 under Blair. Prime Minister Gordon Brown ordered a review of the decision; Smith now proposes to undo the earlier change.

Smith told MPs today that skunk accounted for four-fifths of the cannabis seized on the streets and the drug was more than twice as potent as in 1995.

But the Advisory Council on the Misuse of Drugs reported that the health dangers from marijuana did not justify placing it back in the higher category. It said the scientific evidence pointed to a ``probable, but weak, causal link between psychotic illness, including schizophrenia, and cannabis use."

Smith, however, insisted that tightening the restrictions was necessary.

"There is a compelling case for us to act now rather than risk the future health of young people," she said.