I'm not an expert, but this looks like Wavy St John's Wort to me, one of the flowers listed in the citation that makes our nature reserve, Popehouse Moor, a site of special scientific interest. I'm not familiar with the flowers typical of culm grasslands, so I keep looking out for new ones, especially the rare and special ones.
Ironically, this one wasn't in the reserve - and I haven't spotted it there yet. It was by the carp pond. Many people know St John's Wort as a treatment for depression. I guess I'm lucky I don't have to actually consume it. Just going outside in the sunshine to look at it is a pretty good tonic.