Eurgh, and I have to drive down to the London area in that time period. At least I'll be able to head straight back to the relative cool of the North Wales coast...
Well, I drove down on Monday, stayed the night near Gatwick, then drove my relatives back north again, with no serious issues. Someone suggested I was unlucky to be busy driving on the two hottest days of the year, but I countered that I was quite happy to spend them sat in an air-conditioned car, thank you very much. (The first car I've owned to have it!)
The eleven-year old diesel had to work hard, though. It felt a low on power and asthmatic when the built-in thermometer was reading over 35 degrees (highest indicated was 37.5 on the M40 in late morning), and the gearstick wouldn't spring back left/right in the neutral position in the high heat. The poor thing was a lot happier this afternoon after we passed Birmingham and turned for the relative cool of the Welsh border.
Early morning in Crawley/Gatwick felt odd, as given the low sun and high heat my head said it should be late evening. (The patchy sleep in the non-aircon hotel with safety-catched windows didn't help.) But the weather I found when stopping for lunch in Birmingham, of intense dry heat and a stiff wind, was a memorable experience as I quick-marched across the car park.
6+ months ago, when planning this trip, I decided against meeting the family by train, due to the relative cost of return train fare and fueling the car. Recent diesel prices may have killed that price advantage, but I've ended up happy not to be trying to use the rail network today, given how rickety the service out of London turned out to be.