LIDOBenStansall:Getty

A man swims in the Serpentine Lido in central London, on July 1, 2009. The heatwave warning alert was raised from level two to level three on Wednesday as Britain gets set for more baking temperatures. Level three means high temperatures are reached and sustained in one or more regions, with two consecutive very warm nights and a hot intervening day. By Ben Stansall/AFP/Getty.

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