Hiya Tom, £215 is a good budget for open back cans. You are right in there with some great models.
The sound signatures differ quite a bit and so you need to go and listen to see what bast fits your idea of sound and the music that you listen to.
These 3 should give you somewhere to start.
Beyerdynamic DT990 pro
Sennheiser HD 600/650
Grado SR 225i
They can all be had for the sort of money that you quoted on line.
Fot my two pennorth, as you can see I have the lowly SR60 grado and my son has the DT990pro and we swap back and forth quite a bit. I tend to prefer the smooth grado sound and find the DT990 a bit bright at the top end, but my son preferrs the DT990.
I suspect that I would lean towards the SR225i on this basis. Heck I might even go out this afternoon and have a comparison.......but I really cant afford to be buying more headphones

Have a listen and let us know