I moved to my present house about 6 years ago. When we came here there was an 11Kv power cable right avross the back of the garden between me and my field. My next door neighbour decided he did not like the cable obstructing his view so he got the Elec Co to bury the wires and take down 3 poles. I had no objection of course as it got in the way of my helo approach. It cost him about £10k to get them to bury around 250 metres of cable and take down the poles plus moving a transformer. I contributed £600 for the bit that went past the back of my house. There are pics at
www.rodsley.net if you want to have a look. The red lines are where the power lines are now - previously they went right up my neighbours field and across the top of mine.
I am pretty sure he had to pay the whole cost, but if you get the Elec Co to come in they will give you a quote for free.