To be honest, I think there's more chance that you'll see a thunderstorm in SW England over the coming days than anywhere else, especially as the convection will be mid-level and we have more shear to go with down here. The thunderstorms in SW England will be more organised and widespread though not as severe. However, on the other hand, even though most thunderstorms that do occur further north and east will be severe, they will be very few and far between.
I know which option I'd take.