Can I build a full-width extension over part of shared driveway?

[YourDenimWriter]

I've added photos of my land title (left hand side) and neighbours land title (right hand side), and screenshot of where I plan to build. The black lines are my intended extension, the red dashed lines show where my fence sits.

If I extend as full width of the home, I will block half of my garage, which is fine as I don't use my garage for my car.

Land registry shows that half of shared driveway is within my boundary, but neighbour has right of access, and vice versa with his.

Where it gets murky is, is where does the shared boundary end? For example, you will see from the Google maps screenshot, the neighbour has also extended (perhaps decades ago), and it is full width before the diagonal bit.

The registry states this: "The land tinted pink on the filed plan has the benefit of rights of drainage through the drains and sewers lying under adjoining land leading into the main sewer and a right of way over the part of the side passageway not included in the title."

Any help would be appreciated here.

P.S. A house opposite has done exactly what I plan to do: they have extend out and full width of house amd blocked half of their garage.

Helpful to hear of real experiences, thanks.

So the neighbours extension was done before the current occupants move in, sometime during the 80s I think. I also think that little bend they have in their extension is because the previous occupants did use the garage for their car, so it's easier to go in. No way a modern car fits in there, and even without my proposed extension, the turning circle is small I can't see how a modern car can fit in there or even through the passage. I certainly haven't attempted it.

The Registry doesn't make clear where the side passage actually begins and ends. Technically, isn't the neighbour encroaching by going full width with their extension before the angle?

That was my first thought too. It's a totally mad idea. In any case I can't see you would be allowed to build over a shared driveway. But seek legal advice

If you want to build over a public sewer you will need to get a build over agreement from the company that provides sewerage services for your area. The alternative (if it's possible) is a sewer diversion.
Both cost £££.
That aside. Have you spoken to the neighbour?

But she’s not proposing to build over the shared drive. She’s proposing to extend out from the back of her own property matching the existing width of her own house. The right of way only exists over “the part of the side passageway not included in the title”. I think that’s the part you need to get advice on OP alongside the drainage, to establish what constitutes the “side passageway”.