Inside the key case of my "M" reg 306 1.4 LX is a small electronic chip /
transponder which is part of the security system.

I know that there is a sequence of events, like turning on and off the
ignition together with a combination of pressing one or both of the key fob
buttons at the right time, possibly coupled with pressing the bonnet alarm
switch ... ???

Does anyone know the correct sequence to register a new transponder - or to
reset one that has somehow become unregistered ???

Many thanks.