To be fair, 1458 switched off years ago in London, not an issue that I recall, same for Radio Kent's 1035 frequency which also switched off in the 90s. Both were handed over to London commercial stations.
There was a brief period in late 1993, in between the closure of GLR on 1458 and the commencement of the station that took over (Sunrise?) when the frequency was clear and, after dark, I was able to pick up (in Surrey) all the other BBC Local Radio stations - Newcastle, Cumbria, Devon, WM and GMR - that still used that frequency, just by moving the radio about.
I recorded a jingle each from Radios Newcastle, Cumbria and Devon which I recently uploaded in amongst my compilations of BBC Local Radio jingles from the South East: https://youtu.be/FNG_s_K33Gs?t=1915