According to Nikolaus Pevsner, a society’s architecture is the material evidence of how it views itself. By that definition, the architecture of the British lido in its mid-20th-century prime tells a story of civic aspiration at its wildest, most romantic and optimistic. Here is how Pevsner describes Jubilee Pool, the magnificent saltwater lido in Penzance, which opened in 1935: ‘a subtle Art Deco composition of curvilinear concrete terraces in cool blues and whites’. The cascades, columns, diving towers and bright, sun-reflecting colours of the finest lidos were more than just municipal facilities to encourage healthy activity; they were temples to the new aesthetic and promise of the suburbs.

In his entertaining study of British lidos, Tom Fort has packed his swimming trunks and travelled to lidos all over the country. Some thrive and others struggle with maintenance, bureaucracy and energy costs. Sometimes, all that is left of a once-great lido is a stretch of concrete. Nothing now remains, for example, of the South Bay Pool in Scarborough, the famous Cold Knap Lido in Barry or the Purley Way Lido in Croydon, which at one time had nine thousand visitors a day. Several lidos have been saved by campaigning swimmers and some are designated architectural treasures. Peterborough’s Corporation Swimming Pool is Grade II-listed, a fantasia of dream styles. ‘It has something of the hacienda about it, something of the Greek and something of the Roman, touches of Italianate villa, indistinct echoes of Art Deco. It looks as if several creative minds had contributed their impressions from different European holidays and managed somehow to fit them all together,’ writes Fort.

He dates the first proper lido to the opening of the Serpentine swimming area in Hyde Park in 1930 – the brainchild of George Lansbury, the Labour politician and First Commissioner of Works. But when does a swimming pool become a lido or vice versa? Fort concludes that really a