Suggest you start by getting a quote from Scottish Power to move the main cable, then. You may find that it dissuades you from wanting to have this done, as it will run into four figures, I guess. Unfortunately you can't charge rent for pylons, cable attachment methods on your land if it is only to feed YOUR supply. Clearly if this house was being attached for the first time, it wouldn't be done like that anymore.
The cost of the job is perhaps around £1000 - £500 for the scaffolding, £500 to take the bricks down below roof height and re-batten and tile the roof, inc. VAT.