How is 'near' defined for NDN digging near the boundary? (Diagram)

[BuildingQ]

I live in an early 1970's development of eight house with garages in 2x4 blocks separate from the houses. The house behind us (I.e. not one of the eight) have applied to replace an old single storey extension with a new two storey larger extension. This isn't close to my house but is very close to my garage. The garages are brick built and seem pretty solid, (just to explain they aren't temporary/lean tos etc).

I'm personally not concerned about the end product extension, but don't know if I should be concerned about any damage to my garage during the works? I'd assume not, given anything likely to affect my garage would more likely affect their existing house as it's closer but what if the garage block isn't as robust?

I've been trying to look into the Party Wall Act but haven't found the clarity I need. It just says if they are 'digging near'. I've read people should notify you specifically if digging near the boundary but perhaps that comes once planning is granted?

I would welcome anyone's advice if you have any experience or expertise. I don't really know the neighbour, but they seem amicable. I have no plans to object nor want to make things difficult, just want to ensure my property won't be damaged or that I am adequately protected should anything unfortunate happen.

Key for diagram:
G1-G4 = garage block for my development. Mine is no 4
N1 is the house on my development nearest the neighbour, not my house though
Green Square = site of the current single storey extension
Red Hatched Area = proposed two storey extension
Purple distance = to give scale, it's about 1.5m from the corner of my garage to the corner of their current single storey extension. It's very close.

so 1.5m clearance...I think that's plenty really, room to put a ladder up to do gutters/window cleaning.

It's within 3m, you need a party wall award. Your neighbour should know this, so no harm in asking them if they have appointed a surveyor.

@LaurieSchafferIsAllBitterNow I'm not too worried about the ongoing stuff and the distance is the same today, just the potential for damage during the works.

@Zinnia thank you, do you have a source for that? Sorry to ask but this exactly the kind of thing I'm after. If it's confirmed that within 3m is the distance for party wall act to come into play then I'll try and get my head round it a bit more.

The government has an explanatory booklet on their web site. Just google it. You need an agreement for excavation within 3m of any building. A PWG will agree the condition of your garage before and after the work. You can agree access for work, reinstatement, working hours etc. They cannot start work without one and you can point this out to them. It will safeguard your financial position.

Sorry PWA! If it doesn’t cover what you need, you can inject to it and your neighbour must pay for your surveyor and both parties agree what’s in the agreement.

Thanks @TizerorFizz very helpful. I think I found that but after an initial skim didn't see what I was after. If 3m is specified, I'll have another look for that.