I’ve got a fairly unique light fitting that I quite like. It’s about 20 years old and used to take 10 x 10w G4 Halogen bulbs. At 100w this looks profligate these days, so I swapped the halogens for LEDs. The light is fine, but it kills the DAB radio signal whenever we turn it on. Would it be worth dismantling it and swapping the old transformer for an LED driver, assuming I can find one that physically fits? Would this stop the interference?

I doubt your solution will work as your G4 lED lamps are converting 12vac to DC internally to work so if you change the transformer to a driver then that circuitry in the lamps won’t work.

The LEDs were sold as being ok on AC or DC