Where did Radio 4 come from?

I tried searching and kept getting the same canned statement about "We only need to know the number of interference cases, no details, and no names/addresses." (which surely statistically means bugger all as there's not much way to tell if these cases are even genuine).

There is a reason to ask this - Radio4 is on LW. My mother listens to it and pretty much *everything* from my CRT to the local farmer's milking machine > 1/2 mile away interferes with it. Then there's FM R4 which is supposed to be more resiliant as FM was devised to get around all the problems with AM.