I changed my battery over last week and now the srs lights on fully.. when you cycle the ignition the light blinks momentarily. Nothing showing on diagnostics either . Can’t even find the srs module to interrogate it for some reason .. wondering if anyone’s had similar. Shall try a battery reset today but not hopefully. The fact it’s happened after battery was out points the finger at the yellow connector next to battery surely?

I’ve had similar which was the battery disconnect unit which is connected via the yellow plug you mention. That is a pyrotechnic charge that fires off and disconnects the battery in the event of a heavy crash which you probably know so you need to be a bit careful around it. When I had the problem I had to clear the fault with Allcomms and it would take a few attempts, when Allcomms was clearing it the light would flash on and off and then eventually stayed off. The wires going to the yellow unit connector are a little fragile.
See what the battery reset does , obviously waiting for the sat nav to sleep, I would open the bonnet and wait about 20 minutes before disconnecting as long as everything stays asleep.
What diagnostics are you using?