Suggestions that the supply of the herb khat is linked to the funding of terrorist groups operating in east Africa were dismissed out of hand today by the Government’s own drugs advisers.

The Home Office is believed to be sympathetic to banning the stimulant used by members of the Somali community in Britain, fearing the khat trade is associated with al-Shabaab, the Islamist group fighting in the Horn of Africa with ties to al-Qa'ida. In opposition the Conservatives pledged to outlaw the substance.

But the independent Advisory Council on the Misuse of Drugs (ACMD) put itself on a collision course with ministers by recommending that use of the herb remained legal. It said it had investigated widely whether khat is linked to crime or terrorist activity but drew a “complete blank”.

Its co-chairman, Les Iversen, said: “We pay no credence to this idea – we think it’s a nasty rumour that is going about.”

The ACMD said it found no direct link to medical harm apart from a small number of reports linking khat use to liver damage.

A minority of the council’s members disagreed and called for khat to be banned.

Around 2,560 tonnes of khat was imported to Britain last year – a fall of about ten per cent since 2005. It was worth £13.8 and brought in £2.8m in tax.