Passenger compartment blower running even when car is locked

[Mark in the Lakes]

Hi everyone. My first post & a real head scratcher. 
my passenger compartment heater is going crazy. Blower works randomly when switched on & car running (I believe this may be due to low refrigerant pressure - not checked but wasn’t always cooling properly back in Aug/Sep).

What’s now happening is the fan blows even when ignition is off. No lights on the control panel (if I press & hold the econ switch it will light up but doesn’t respond to any inputs) 

It has even run when the cats been locked up, causing flat battery on a couple of occasions during lock-down. 

Any help appreciated. 
Thanks in advance. 
Mark