Question Author
Thanks to everyone who offered advice, the problem appears to have gone away for now. I refused to give access to the contractor other than at a time which was convenient to me, they declined to accept this and informed my neighbour that if he still wanted to go ahead with the upgrade he would be liable for any extra cost such as scaffolding or a cherry picker. He has declined to pay for this and as such the contractor has told him his job cannot be done by them.
If he had simply knocked on my door and discussed this in a neighbourly manner I would have had no problem allowing the work to be done , but I draw the line at being threatened with solicitor's letters and being told what I can and cannot do on my own property. Perhaps in future he will take the easy route and try talking but I will not hold my breath waiting.
Thanks again, bronzesmith