Airbubba
The UK does not currently have in place any Regulations such as those stipulated by the FAA for monitoring drug/alcohol misuse within aviation, or for that matter for crews of ships at sea. This is an anomaly as I believe both train drivers and drivers of heavy goods vehicles in the UK are subject to testing at initial employment and then randomly.
I am not sure it is either a good or bad idea to have random testing but it does appear to be illogical to have such rules for some forms of mass transport and not others. I believe the Masters of both the Exxon Valdez and the Marchioness River Boat on the Thames had excessive alcohol in their bloodstreams at the time they lost control of their vessels - and their command capability was certainly judged to have been impaired because of this.
The proposed Railway and Transport Safety Bill looks as though it aims to address this anomaly in the Regulations.