The key here is whether there is a wayleave agreement is place. A wayleave is an agreement between an owner of the land and an electricity company. In some cases there are wayleave agreements in place, in which case you can do little - and particularly this is likely to be the case in rural areas if your (and maybe other neighbours) electricity supply came from the wires (even if your supply doesn't now come from overhead).
In other cases there is no wayleave agreement, but I have found it very hard to get the companies to tell you if they have an agreement for a specific pole or not.
Some answers here and you could try talking to these people and you may get some free guidance - but beware that they are a commercial outfit who will want money for solving specific issues.
http://www.wayleave.co.uk/wayleave-faqs.htm