Freelander 2 multiple electrical issues

Hi all, new here so any help/advice gratefully received. I have a 2011 Freelander 2 that has been amazing since I bought in 2018. However over the past few months I started noticing problems. The central locking from the key fob became temperamental. Sometimes it would work sometimes not. Eventually stopped working at all so I tried the spare fobs and nothing. Changed battery in the key fob and still nothing. Then got home late one evening and noticed that having locked the doors with the key, all interior lights stayed on. Footwells, boot, glove box. I ended up taking all the bulbs out. My usual mechanic couldn’t work out the problem so I went to a car electrical specialist who ran tests and confirmed that the key fobs were all working fine but the BCM(?) might be the problem so I’d need to take it to an LR specialist. My worry is that I know from experience that my LR specialist is very very expensive! It’s booked in 21/12 anyway but is there anything I can do myself or anyone local(ish) to Gloucestershire who can help without the need to remortgage my house?

I don't know the first thing about the RL2 but as with any modern car, is check the battery is more than just 'ok' (something that's easy to overlook) and that the car is dry, no damp in the boot, under the carpets etc

How old is the vehicle battery? If it's more than 4 years old, it's not going to be a good as these vehicles need.

The interior lights are a strange one. They are supplied by the CJB (BCM) but take control signals from sensors in all 5 doors.
Do you get a door open warning on the dash?

The fobs transmit a coded signal to lock and unlock, but the receiver might not be receiving that signal. The receiver is in the roof near the rear interior light if I remember correctly.

Really you need to have the codes read. You want a full vehicle code read, which should point to the issue.