SALISBURY'S GW Pharmaceuti-cals has landed a multi-million- pound marketing deal for its pioneering cannabis-based treatment for multiple sclerosis sufferers.

GW, operating from Porton Down, announced that it had sold the UK marketing rights of its drug Sativex to German healthcare giant Bayer.

On top of a £5m signing fee, GW is to receive milestone payments of £25m once the treatment is given regulatory approval and will take a share in the revenues from sales of the drug.

GW, which grows 40,000 cannabis plants a year at a secret site in the southern counties countryside, hopes the mouthspray will be on to the market by the end of this year.

Clinical tests on the treatment have already been successfully carried out but before the drug can be given to patients it must receive clearance from the Medicines and Healthcare Products Regulatory Agency.

A licence application was submitted in March and tests are currently taking place to assess whether the drug can help cancer sufferers.

Chairman Geoffrey Guy said: "It is GW's first commercial collaboration and marks the start of a new phase in the company's history.

"As a leading global pharmaceutical company, Bayer is well placed to maximise the market opportunity for GW's product."

Because of its cannabis content, Sativex will require a change in the law but Home Secretary David Blunkett has already indicated that he would be willing to make the amendment if the drug received approval.

The deal gives Bayer the option to negotiate marketing rights covering other European Union countries as well as a selection of other places.

GW is poised to examine the possibility of entering the market in other commonwealth countries such as Canada, Australia and New Zealand.

The company employs 100 people across the UK.