Yes, this is going out to all licensees of transmitting equipment. Basically it seems to be a large scale ass covering. It's known that exposure to non-ionising radiation can cause damage and they seem to be making the operators aware that they could be liable for any injury if they haven't made the calculation and taken the necessary steps to mitigate the risk.
It seems, to me, that they are trying to ensure that nobody can come back to OFCOM and say you never told us about this, and perhaps hold them liable.