[flaxton]

Melanie
I think you are spot on with S. gravellei but I am not so sure about your X. impolitus. (It was for a time put in Xerocomus by some people but I think it is now accepted as a Boletus.) It is normally a much more robust fruitbody and when it is cut there is a distinct yellowing just under the cuticle of the cap and stipe. The stipe is lemon yellow at the top and punctate over the full length. Your specimen looks to have a striate stipe without the "dots".
The lack of colour change with ammonia probably rules out B. subtomentosus and I would suggest B pruinatus.

Mal

Ps I have a new key for Xerocomus so PM me and I will send it across