Correct Attak,
As a Groundworker, I dig a lot of holes!
Basically you have to ensure your not undermining neighbours (or your own foundations)
Therefore You usually keep a metre off neighbouring walls, which is roughly the 45 degree thing.
What a lot of people dont realise on these kind of projects, is the amount of muck (earth) you'll be shifting, you could be talking about 10-20 20 tonne lorry loads... at £200 a pop, its not cheap.
You then have to tank it (waterproof) it, and run electrics etc to it.
And above all else, it has to be safe..... Often means trench sheets, or a big box in which to work in, even these can be about £200 a week to hire......
So yeah, its feasible, you. will need a big digger, and anything can be done for the right money, but as they say there are £1000's in the ground and £100's above it....