Its one of the biggest pitfalls when quoting for or carrying out electrical work edpecially in older properties.
The biggest excuse they use is "its looped of next door and they neen to be in for us to pme it".
Under the old 16th edition, it wasn't reccomended that a smoke alarm should be connected to an rcd. And I would mention that to them that if there were a loss arising from smoke alarms not working due to loss of power and flat batteries. They may be called in court to share or take the blame for not supplying a reliable power supply intended for public use.
Within a week I would have a date for them to do a pme. The trouble is they keep changing the number for the network operator.