Well.. 2 issues I suppose.
When they're first installed they provide full technical spec on them, and have to demonstrate that the antennae would comply with the WHO/ICNIRP guidance.
If anyone is remotely concerned that the information provided is suspect, or that the radiation exceeds the threshold, they can be investigated.
Second issue really is that with the prevalence of street masts (sometimes disguised to look like lamp columns) round here I reckon that it's fairly unusual not to be within 300m. Think our nearest is about 400m. But then we're none too far from the Crystal Palace TV mast, which has a massive range.
I feel sorry for the authorities as in the Local PLanning authority dealing with the consultations from telecoms companies. They have their hands tied to an extent - impact on health cannot be used as a ground for refusal. Has to be on siting and appearance - and that is hard to justify in some cases as the companies become more and more savvy at disguising them. But then on the other hand, if it has been decided that regulated masts do not have an adverse impact on health, and I am no scientist, why should I not trust that there is no impact on health? I can't prove otherwise.
For an example of complete double standards, we were decidedly put off a prospective house by it being slap bang next to a massive power line. Even though the owners had get an independent survey in an attempt to win over potential buyers. Looked awful, but there's always a nagging doubt isn't there.