Coastguards are today warning members of the public to stay off St. Catherine’s Island, near Tenby, after three Polish brothers found themselves trapped on the outcrop.

The brothers, on a day trip to Tenby from Tumble, had climbed up onto the island through caves. When the tide came in they found themselves marooned, their exit barred by railings and locked gates.

Tenby police and coastguards were called to secured buildings on the island at about 3.30pm. Coastguards managed to release the gates and the three youths were led to safety.

The fort on the island was built in the 1860s to protect Pembrokeshire from a possible Napoleonic invasion. It was sold in 1907 and became a lavish private home. It has also since housed a zoo but is currently unoccupied, with the buildings succumbing to time and the elements.

"St Catherine’s Island is privately owned and is not accessible to the general public, hence the locked entrance gates," said a coastguard spokesman.

"The buildings on the island are in a severe state of decay and highly dangerous," she continued. "The island also becomes completely cut off with the high tides.

" Although the island looks tempting do not climb up onto it, as the chance of injury or prosecution for trespass are high."