The operator of Britain's first offshore off-licence vowed today not to give in to pressure from Customs officials.

The owners of the Cornish Maiden, 12 miles off Hartlepool in international waters, claim they can sell cut-price cigarettes and alcohol as they do not charge customers duty because it has already been paid in Germany.

But Customs officials insist booze-cruisers must declare their goods and pay UK duty when they arrive back on dry land or face losing their bargains and even their boats.

Businessmen Phil Berriman, of Stockton, Teesside, who runs the operation with lecturer Trevor Lyons, of Newcastle-under-Lyme, Staffordshire, said a Customs ''cutter'' vessel was ''circling'' the Cornish Maiden and putting off potential buyers.

He said officials intercepted him in a high-powered inflatable and asked if he had goods to declare as he came back to land from visiting the Cornish Maiden today.

He said newspaper reporters had been out to buy goods today but he did not know if they had been stopped.

Mr Berriman said Hartlepool Marina was ''full'' of Customs officials in unmarked cars looking for his customers to quiz.

''They are stopping everybody. They really are putting the pressure on.

''But this will turn into a protest. If they want to spend hundreds of thousands of pounds, they can do. But they are in the wrong and they know it. ''We are definitely not giving up.''

Last month Customs returned goods worth more than £100,000 which it had ''detained'' from the off-licence operator's previous vessel, the Rich Harvest.

A Customs spokesman said today: ''We are monitoring the situation but we will not make any comments about operational movements. We haven't detained any goods so far today.''