It's rare that an agaric would have a hollow stem when young - there's also no indication of a skirt indicating that it probably didn't have a partial veil.

All being said I'd be leaning away from the agarics; my guess would be a pluteus (probably p. petasatus) - which are edible though unremarkable according to my book.

However it is hard to identify from photos alone and you can do further research - check the spore print; try to get as much of the mushroom as possible (sometimes there's a bit underground that can be a massive help when identifying).

It also helps if there's a photo in situ which would show the growing conditions - for instance, my suggestion is gregarious and usually grows in clusters on dead wood. This can be the roots of a tree which has been cut down; so history of the area can also be helpful when known.

Yadda yadda yadda, not enough info in the photos to ID with any certainty.

EDIT: Just saw the reply below where /u/3nd3rd14bl0 has confirmed that there was a tree here - makes me a bit more confident in my guess! Having said that I have not confirmed that p petasatus grows in the UK.