My God, i go away for 2 days and this thread has descended into anarchy
i was in "That There London" but that is a different story.
You say you want to move the cable because you want to knock the wall down. Your problem is that from the pictures of the service head, it is an old cable and a new head, so when they fitted the new head they must of deemed the cable to be fit for use as it stands.
You have asked for a quote to move the head but the DNO deem, that to move the head they will need to replace the cable because as in a previous post, if you move that cable, there is a good chance that it will fail and they have quoted you the prise to do so.
Even if you can find a contractor who is authorized to carry out the work by the DNO, you will find that the quote will probably be much the same if not more. minimum of 2 men on site, permits to obtain, cable, joint, ducting, re-enstatment, testing and then you will need an electrician on site to reconnect between the new location and the old.