A woman out for a walk stumbled across a black bag containing about 12kg of the drug at Shanklin on New Year's Eve.

She took it straight to a police station, Customs and Excise officers said. Further forensic tests are to be carried out.

A Customs spokesman said that it was "quite a big find" but no arrests have been made.

Strong tidal currents

"We are very pleased that she took the trouble and interest when coming across something like that and then handing it in to the police.

"Because of the weather the sea has been so rough and the tidal currents are strong on that side of the island which means the bag could have come from all sorts of places."

A search of the beach failed to find any other packages.