Plymouth mil is more than likely who the civi controller phoned.
Its always worth having a list of the mil frequencys.
If I didn't get a reply on plymouth mil the next one I would try would be london mil. Then london info.
Sometimes the civi controller won't have the time to find out for you or all they will say is its hot.
Its actually hellva lot of work for the controller to find out etc And I know they provide a service etc. Personally I don't think it is unreasonable to expect the pilot to have a bit of forethought and just speak to the mil direct as they have the yes/no call anyway.
Another frequency I would have in your back pocket is western radar another bunch of fine people. If you were a bit further west.