not at all - it can be difficult to explain physical circumstances in text. I believe I now very clear on the arrangements thank you.
The position based on the extracts you have kindly provided from your title is that there is a passageway between your respective properties and each of you appear to own approximately half of that passageway divided down the middle in line with the dividing boundary line and over which respectively each of you have a right of way over the others parts allowing each of you effectively to pass freely over the entire width of the passageway by combination of owning half and having a right of way that the other half. Such arrangements are common in respect of shared passageways.
It therefore follows, that an attempt to build over that part of the passageway over which you enjoy a right of way would amount to a derogation of your rights of way over the passageway. In other words, if he seeks to build over such part of the passageway over which you enjoy right of way, this would infringe upon your right to pass over it and as such, you could seek to resist such building if necessary, by way of injunctive relief.
Ideally, you would be able to negotiate some form of settlement with your neighbour which is agreeable to both of you but ultimately, if you are unable to reach agreement, then you would be able to consider applying for injunctive relief in the County Court to prevent him from proceeding with the proposed work so far as it delegates from your rights:
in addition, if he is planning to excavate within 3 m of your building where he is laying foundations lower than your existing foundations, then he would need to serve the party wall notice upon you before commencing works quite separately from the above