Comparing the GFS 00Z to the 06Z in the more reliable time frame:
Monday 00Z:
Monday 06Z:
GFS trending a degree or two warmer in the south, much the same elsewhere, though perhaps a degree or two cooler in parts of the north.
Tuesday 00Z:
Tuesday 06Z:
GFS trending warmer in the south east, with London potentially hitting 30 degrees, but cooler in the north probably with rain/thunderstorms.