Planning, 'boundary line to be agreed with neighbours?'

[BogwashBarry]

I'm in a 30s semi and my neighbours have submitted planning permission for a large extension across the back & open-up internally. I thought planning diagrams had to include exact measurements of the proposed new build? -So that all parties involved know exactly how big this extension is going to be? On my neighbours plans (which the council have sent me details of) it just says 'boundary line to be agreed with neighbours'. No-one's come to me and said 'we want it this big' & isn't it a bit unscientific anyway? I thought the whole point of going through planning permission was to specify exactly what is proposed? And right now I have no idea. The diagram also shows the new extension adjoining my exterior wall so how do I invoke the party wall act? I believe they have to pay for someone to represent my interests.

Hmm - you don't have to own land in order to obtain planning permission for it. I wonder whether your neighbours want to negotiate to purchase some of your land to achieve what they want for their house. Do the title plans and title registers for both houses show the boundaries/refer to the boundaries between the properties?

The problem is that the lines on a title plan sometimes don't match up with what is on the ground - measurements aren't given so things can be rather imprecise. This can often be the case with older properties.

Have they even discussed their plans with you? Ask them or their agent (named on the application) to clarify the boundary matter in writing.

The party wall stuff would come afterwards.

The drawings will be drawn to scale (although measurements are usually included as well).
It should be possible to work out the extent of the extension by scaling off the plans, and then measuring out the extension on their property. Ask your neighbours and/or their architect to show you were the proposed extension is going.
Exact boundary lines are extremely hard to define. If you are a standard 1930's semi, with gardens running straight to the rear, then it would normally be the mid point between the two properties. I take it that your neighbours have not served notice on you prior to making the planning application. If they were planning on using land that they did not own, they would have to do this as part of the planning process.
Party Wall Act is quite complicated - I don't think you can invoke it. They have to serve notice on you if the Act applies. It is separate from Planning law and Building Regulations.