When the drug user is found at Colleano's Mr Colleano indicates that 'they cannot call a doctor as the doctor will inform the police', indicating that Colleano's has committed an offence. This would not have been so.
The Defence of the Realm Act (1916)(Regulation 40B) made it an offence to use opium based drugs (originally for soldiers but was then extended to the general public 2 months later).
The Dangerous Drugs Act (1920) made it an offence 'of being an occupier of premises permitting the smoking of prepared opium'. As the episode is set in 1919 - reference is made to the Peace Treaty, Colleano's had not committed an offence.
Whilst it would have been preferable not to have the police present, it is difficult to believe that he would have said not to call a doctor before making sure the customer was not seriously ill if no actual offence had been committed.