When the entrance to a theatre in London’s West End was discovered to be smeared with blood and faeces one day in March, a distress call went out to the headquarters of Ben Giles, a 49-year-old veteran of the extreme clean, who is based in Cardigan in Wales. Decades earlier, as a young know-nothing, hired by police to clean vehicles, Giles laboured for hours to remove fingerprint dust from the interior of a stolen car – work that now, with the experience of innumerable litter-dashed, liquid-sodden, gunge-roped scenes, would take him about 30 minutes. Job by job, he figured out when to scrape or sand, soak or fog, preserve or dispose. Boilersuited and plastic booted, Giles learnt how to eliminate most evidence of spillages, collisions, haemorrhages, severings, explosions, fires and…