they use them for sight-seeing while the Tall Ships are at the Island.

The Department of Agriculture and Fisheries issued the caution to deter fishermen tempted to hire out their boats to members of the public wanting to watch the Parade of Sail.

Many commercial boats are imported into the Island duty-free but there are strict conditions placed on their use.

The boats are restricted to "commercial fishing or scientific research or for hire or reward for commercial fishing or research''.

The Collector of Customs has the right to confiscate boats and fine owners up to three times the vessel's value if fisherman flout the restrictions.

A Department spokesman warned that fishermen will still be hammered if they trail a fishing line over the stern when the real purpose is to take sight-seers.

The spokesman said: "The Collector of Customs has confirmed to us that HM Customs would view any other commercial use as illegal.

"In the circumstances, we feel we must warn members of the public and, especially, fishermen themselves that the penalty for such unauthorised use of a duty-free vessel is forfeiture of the vessel and a fine of up to treble its value.

"While a collector has some leeway under the law to fine people less than the maximum, he has no discretion where seizure of the vessel is concerned.''