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If you go for a dip in the Channel these days, the worst thing you face is raw sewage or being hit by a ferry.

But 50million years ago, it was more the threat of giant crocodiles, great white sharks and sea snakes that would have preyed on your mind.

In those times, the area between Paris and London was a tropical lagoon teeming with the most diverse marine life on the planet, say Natural History Museum researchers.

Our shallow waters were more akin to the seas around Indonesia or Thailand today, with their hot and humid weather, too. The only creatures missing would be mammals such as whales and dolphins, which were only just evolving, said the museum's palaeontologist, Dr Jon Todd.

The discovery followed a study, published in the journal Science, of how tropical hotspots move around the planet in line with the shifting of tectonic plates. Sadly, much like any decent weather, the warmth moved on.

The sticky climate changed completely over the next 30million years as the plates moved and built mountains in the Middle East.

European waters were isolated from the warmth of the Indian ocean and the heat moved to the more familiar location of south-east Asia.

Fossils at the museum proved a critical piece of the puzzle, said fellow palaeontologist Dr Ken Johnson.

'They allowed us to map out the changing geographical spread of tropical biodiversity as the hotspot hopped around the world,' he said.