Excavation of tunnels and such should just come with a chance of finding artifacts, but it only materializes with the right culture tech unlocked (before some point, buried treasures were just scrapped or sold, not put into museums).
If you want confirmation, the easiest bits to "check" are Aylesbury and Coventry. London and Birmingham are too big for the features to stand out.
Here is the official HS2 map: https://www.hs2.org.uk/map/?mapView=9_52.0744_-1.8347
British NIMBYs seem unusually strong, even in a world of NIMBYism. Best wishes to the British in defeating the Midsomer Historical Society of Bat-Loving Cranks, which apparently controls the deep state over there.
As opposed to a foot axe I assume
> and 19th Century gold dentures
Ah, them classy 19th Centurians!
However, some significant distinction should be made for what is actually meant here. For such historic finds "hand axe" often means a stone tool with two faces and shaped like a tear drop / round-bottomed triangle. With the 'bottom' face shaped to a crude blade, and the 'top' 'sides' made into a grip. Note there is no shaft, and the way it is used is speculative and likely very varied, as few other tools existed.
The proto-axe if you will.