It looks to me like the GFS keeps both the polar and russian cold pools away from england, however, the GEM seems to bring both over blighty on Sunday...and keeps them there for a significant period.
The GFS shows some precip/convection around the same period over the London area shortly before (-6h), but this is mixing models, so not very accurate.
My feeling is that the best chance for a major event, based upon current output is Sunday daytime. What do you guys think?