Subjective I know, but a good run of 27C days with a couple of 30C days is what I would consider a heatwave. At no point on 06z does London even have a day at that level. Most of it looks average or slightly above - not really a heatwave. And the poor east coast folks will get punished again. Maybe not with clag, but with disappointing cool temps for high summer.
Caveat - the above is based on the 6z run.