UK avionics demise due to: the prevalence of multi-nation aircraft programmes where political necessity forced a third-party avionics choice
In military aviation we can still see the remains of the British avionics industry, just as we can see the remains of our airframe capability in Airbus. However, in civil aviation where I work, there are three choices for avionics - Rockwell Collins, Honeywell and Thales. GB is limited to producing a few nice bits of very accurate test equipment.