Hidden below St George’s Wharf in Vauxhall, down the road from a now defunct gay sauna, is Floatworks, a wellness centre that offers ‘floatation therapy’.

Sensory deprivation tanks can be found in most British cities — in bohemian towns like Bristol and Brighton, but also in Birmingham and Belfast. The concept is simple enough: people are locked in an unlit pod and lie there with nothing but their thoughts.