AN eagle-eyed reader has solved the mystery surrounding the origins of an offshore structure in Poole Bay that left cliff-top residents and sightseers puzzled for days.

Several seafront home owners who contacted the Daily Echo assumed that the giant platform, clearly visible between Bournemouth and Boscombe Piers, was connected with the proposed Navitus wind farm.

However, just weeks after Bournemouth councillors objected to plans for a 100-metre high meteorological mast in the bay, wind farm developer ENECO insisted that the strange structure was nothing at all to do with its plans.

A spokesman for the Crown Estate, which owns the seabed, said he believed it was a jack-up vessel and two other craft operated by the oil and gas industry.

But both BP and Perenco, which bought Wytch Farm and Beacon Oil Fields, denied any knowledge of the structure, along with Infrastrata, which has an exploration licence block off Old Harry’s Rock.

Local councils were perplexed by the sea structure.

However, a Portland Coastguard spokesman said: “It was a rig passing through, sheltering from bad weather.”

After some research, a reader concluded that the structure was a Seafox 7, a self-elevating accommodation and maintenance support unit which can operate in water depths of up to 45 metres.

As well as being suitable for supporting installation activities in the offshore wind farm market, the unit can be used for the installation and construction of platform ‘decommissioning activities’.

The state of the art accommodation includes a cinema, gym, satellite entertainment system with hospital and laundry facilities as well as a helicopter deck.

Its operator, Dutch-owned Workfox BV Ltd, confirmed that the Seafox 7 had been in Poole Bay.

Spokesman Alexander Eijgenraam said: “She stayed there to await suitable weather conditions to allow her to continue the tow to the Irish Sea.”