Not long ago, if you asked discreetly in the right Hackney pub, you would be put in touch with a character called Syd the Squatbroker. For as little as £150, he would gain access to the roof of an abandoned council tower block with a set of fireman’s keys. Then Syd (nom de guerre of a carpenter from Harlow) would abseil down to a window, gain entry and open an empty flat.