Flowers mostly 4-petalled, but a few with 5, all about 20mm across. Low to the ground in slightly acidic woodland glade.
No interactions present.
Was it fertile? Hybrids with the other two species (reptans and erecta) are not rare. Another tricky genus!
I agree it could be a hybrid, which is why I went for "It's likely...". Plenty of erecta on the site, but have not seen reptans there(not that that need matter). I'll have a look for fertility next time I am there...I was mainly doing flies, today.
My Flickr photos...
Looks like a hybrid to me too. P. x mixta/anglica.
Lat/Lng: 53.88803380063, -0.89153409004211
OS grid ref: SE729441
Woodland Trust reserve