I'm not convinced there will be any forcing mechanism.
I think the MetO have been overly excited in issuing the warning update they have. No model (I've seen) suggests storms/downpours will continue much through the afternoon, with the exception of perhaps EA. Already a new cell appears to be gathering around Ely, but little electrification at the moment.
That said, the link to the Tony Gilbert analysis (posted by someone yesterday) over on another forum, suggested that potential could exist up until around 17z across the SE...I was dubious then and remain so currently (despite the deeply humid feel and slight signs of instability aloft).