Like a volcanic crater emerging from the sea in the flat landscape of The Wash, a strange island – part of an ambitious 1970s experiment – has been a source of intrigue, says Rachel Buller.

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From the air it looks like an eerie alien landscape, emerging from beneath the waves. From the land, it catches your eye like a strange volcanic mount, breaking the otherwise flat horizon of the Fens and The Wash.

But this secret circular island is no natural phenomenon.

The science fiction-esque ‘Outer Trial Bank’ is the result of a hugely-ambitious and expensive feasibility study carried out it the 1970s to test plans to build a freshwater reservoir system in the middle of The Wash.

The raised crater, 280 metres in diameter and 14 metres high, was designed to hold millions of gallons of water to prevent predicted shortages in the 21st century.

This Monday, the BBC1 programme Inside Out will give viewers a rare glimpse of life on this isolated and secret island and show that while its original purpose may have failed, the same cannot be said for its new incarnation.

For this weird moon-like environment – an intriguing lasting legacy of what might have been – is now teeming with the birdlife as home to 7,000 gulls.

Inside Out is on BBC1 on Monday at 7.30pm. Want to read more? See the Sunday supplement in Saturday’s EDP.