A restored pleasure cruiser is at the centre of a criminal investigation into a tragedy involving the deaths of two children on Bournemouth beach, the Telegraph can reveal.

The Dorset Belle has been impounded by Dorset Police and a man in his 40s described as being “on the water” at the time has been arrested on suspicion of manslaughter.

A 12-year-old girl and 17-year-old boy were pulled from the sea with “critical injuries” on Wednesday, before being rushed to hospital where they were pronounced dead.

RNLI lifeguards had dashed into the sea after ten people found themselves at risk of being swept away by a sudden and strong undercurrent, but exactly what caused one of the worst incidents in recent history at the British seaside is not clear.

The Dorset Belle left Bournemouth Pier at 4pm yesterday, according to online tracker MarineTraffic, just seven minutes before the first call to the emergency services was made to report an incident in the sea.