Digging pond between 2 garages - planning and general questions

[Greggerly]

hi guys
part of my garden is sandwiched between 2 garages (mine and neighbors). The garage wall is part of the partition wall between the properties. I'm planning to dig a pond in this space. I was planning my pond to be circa 2 metres deep. Couple of questions:
- how close to the garage can I dig? what's safe and how large should I expect the footing of the garage to be?
- do I need to submit anything besides section 6? (pond will be within 3 meters of the partition)
- pond walls will be pretty much vertical. do I need to support the walls while excavating?
- considering the depth of the pond do i need to reinforce the walls? Its a pond liner vs hollow blocks wall question. Cost-wise liner is much more affordable and less labor intensive. But if there is any risk to the adjacent structure I will go with the hollow block option.
Its worth adding - I'm in Hampshire and my house sits on heavily compacted clay.

thanks
Greg

 

[Doghouse Riley]

Garages are rarely built on anything other than a concrete raft of no more than six inches if that.
Clay is awful stuff in which to dig a pond, it might need shuttering.
Back in the days when I kept koi, I read tales of the sides falling in during a build.