Thanks for your enquiry.
On the basis that it was agreed that you remove the wall, I don't think it would be wise for you to now put up a new wall. However, the agreement was that you do this work and he pays half of the cost. Hence, when your neighbour's Solicitor gets in touch with you in your capacity as Freeholder (which he will have to so he can satisfy the Buyers Solicitor that all ground rent has been paid up to date, and the Buyers Solicitor will need to know your details as a Buyer's Solicitor is under a duty to serve Notice (called a "Notice of Transfer") on the Freeholder that there is a new leaseholder), you can confirm that the sum of £600 is outstanding from the neighbour. You can also stipulate that you won't accept any Notice of Transfer from the Buyer's Solicitor until this sum has been paid. This will therefore force the issue and I would imagine that your neighbour's Solicitor would pay the £600 on completion of the Sale.
I hope this assists and gives you a practical way forward.
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Apologies- I thought your neighbour was selling.
On the basis that he has not kept to his side of the agreement, you are indeed legally entitled to reinstate the wall.
Alternatively, if you left matters as they are, the only guaranteed way of getting your monies back from him would be to issue small claims County Court proceedings against him. You can do this online, but it is whether you want to risk the possibility of going to Court and winning your case. Here is the link- https://www.gov.uk/make-court-claim-for-money/overview
Other than the above, you could just sit tight and wait for him to eventually sell and raise it then.
I hope this helps and sets out the legal position.
Hi, thanks. Hope it all goes well for you.