Odd isn't it. My local forecasts is pretty much the same and it was updated at 4pm, if anything it sounded more severe than the morning update. I was reading it, checking the radar, checking the temps, checking lightening sites and thinking really met office are you sure about that? It seemed obvious by then that the cloud hadn't cleared preventing temps from rising, I was forecast 25 it made 20, preventing convergence which prevented convection, preventing storms from forming. Ok not as simple as that but you get the idea. I guess they were let down by whatever models they were using or relying on them too much. I'm not particularly having a dig at the met office, I think they do a fantastic job most of the time, but this forecast was wrong before it was written.
Of course I shall take it all back if I'm woken by a massive storm at 3 in the morning.