The cell in the photo is actually not the right mover that Paul mentioned yesterday. It was taken a couple of hours later but in pretty much exactly the same spot as the earlier cell. On radar (and from a distance, I was observing from a hill about 25 miles away!) it didn't look massively organised but that pic definitely does suggest otherwise.
I need to check exact times with my friend as she said it was taken at 'about 7.30', looking back at the radar sequence I think it might have been a bit later though as it looks like it really intensified at about 7.45.