......."and they informed me that they could not sell on this strip of land as they had only just received the transfer of it from the developer' - well that's bull for starters - they may not want to sell it to you but recent acquisition of it is not a reason in itself.
'How can I adopt a metre of this land away from the wall of my house and fence it off to protect my wall and cables from this vandalism?' - just do it and see what happens. Start small - a row of stones perhaps, now start mowing it, then maybe a small picket fence. The worst that happens is you will asked to remove it. However you will never permanently own it that way if it is actually registered land at the LR. It may not be - it may have been adopted as part of the public highway (verge).
'Is there a way in which I can buy this land and what is the process for this.' - depends on the actual ownership; if local authority owned, yes - they sell it to you - but they don't want to play that ball-game. If part of the highway (verge) then 'no' - you'd just have to try and take possession over a period of time.