Hi which Atterberg tests determines the NHBC soil classification for domestic foundation depth due to trees (NHBC) ? 1 stage or 4 stage tests? £35 ones or £190 ones approximately? If I don't do it then the inspector assumes worst soil type?

Does this shed any light on it?

 

https://www.newbuildinspections.com/wp-content/uploads/2024/07/NHBC-Standards-2024-4-2-Building-Near-Trees.pdf

I haven't done one, or had it done, for decades.

Can you describe the ground? 

See the soil deviations in that nhbc guide. Is it clay / silt/ sand or whatever. 

Soft / hard?

Use everyday terms