Yellow wild flower for ID please.

Yellow wild flower for ID please.

Observation - Yellow wild flower for ID please.. Description: In a clearing in our wood there is this little yellow flower. It is only a couple of feet away from some Slender St John's-wort (The last picture) and it has a bit of the form but I am not sure. It is East Sussex and the soil is sandy, acid and quite dry

In a clearing in our wood there is this little yellow flower. It is only a couple of feet away from some Slender St John's-wort (The last picture) and it has a bit of the form but I am not sure. It is East Sussex and the soil is sandy, acid and quite dry in that area. Bracken, Bramble, Wood Sage and Hard Fern are the other dominant plants. Thanks for looking.