Mark Groombridge, 41, made sales of £630,000 by selling the anti-impotence drug without prescription at £15 a tablet.

Recorder at Stafford Crown Court, John Maxwell, said a jail sentence was necessary to deter others from breaking the law in the same way.

Groombridge was also disqualified as a company director for seven years and made the subject of a £258,000 confiscation order.

You have deliberately flouted the law and you have made substantial profits from this

Judge John Maxwell

The businessman had admitted five charges under the Medicines Act at an earlier hearing.

The judge described the medical questionnaires Groombridge's customers were asked to fill in as "a sham".

He said: "It's obvious to me that you knew perfectly well that a prescription was necessary.

"The mischief that this law is designed to prevent is the risk that may arise from the use of Viagra.

"You have deliberately flouted the law and you have made substantial profits from this."

Internet adverts

The court heard that the married trader had founded his e-business, Menscare UK Ltd, in September 1999 and placed adverts in various magazines offering Viagra for sale.

After his arrest, Groombridge, of Balance Street, Uttoxeter, had falsely claimed that completed medical questionnaires had been sent to a doctor in the US, who then provided prescriptions.

The hearing was told that Viagra worth £100,000 was seized by officers from the Medicines Control Agency in September 2000.

The judge ordered the haul, which has now passed its use-by date, to be destroyed.