Found on the outskirts of deciduous woodland, in an open and very disturbed area.
No interactions present.
Not a plant I'm very familiar with, so didn't think of this - having just had a look on google images, I think you may be right... certainly the wide leaves and reflexed petals look closer to Erythronium.
I would bet good money it is Pagoda (E. tolumense hybrid????). Erythroniums are reasonably commonly grown in UK gardens - there is a clump of Pagoda a few feet from me now.
I had a bit more of a look online and in a couple of gardening books and I agree with you about genus - I really don't know about varieties, hybrids etc beyond that. It's the 'garden escape' gaps like this in my plant knowledge that tell you my wife's the gardener and I'm the one who goes rummaging further afield :)
Agree this is almost certainly a dog's tooth violet. Should know ,used to sell them !
Lat/Lng: 51.542348314403, -0.78787744045258
OS grid ref: SU841833