A JACK-UP platform sighted off Barry’s coastline was an energy firm’s seabed investigation exercise for Hinkley Point on the opposite side of the Bristol Channel.

Excalibur, as the structure is called, is drilling investigation boreholes in the Hinkley Point area for eight weeks moving regularly between planned points.

It is operating 24 hours a day, seven days a week and supported by a tug, named the DMS World, for manoeuvring.

The jack-up measures 60 metres in length by 32 metres wide.

It has a 4.24 metre deep hull, coloured orange and black.

Mariners are requested to keep well clear and pass slowly, particularly when the craft is afloat and manoeuvring.

A listening watch is maintained on VHF maritime channels 16 and Excalibur's call sign is YJXQ 5.