Yes, Rabbit, this is a bit more complicated than it seems.
Stockport M.B.C do not support the erection of mirrors at blinds spots. The reason given is that a mirror gives a distorted image and is not a true reflection, pardon the unintended pun. Thus actually hindering judgement and not helping it. Having said that, there are a few that have been erected in the area either a long time ago or in defiance of this refusal.
My understanding of the situation is that in the event of an incident(god forbid) your insurance claim may not be as straightforward as you think. So wise to check with your insurers first. As if that's not bad enough the owners of the Telegraph Pole could have a liability in the event of an accident. So they will almost certainly refuse permission.