It is going to be hotter in London today (Wednesday 26 June 2024) than places in the Med. Temperatures should be around 31C by this afternoon - that's 88F for those in the 1 country in the world that still uses Fahrenheit. It will be cooler tomorrow (Friday).
To escape the heat, it will be a bit cooler on the coast. I am not a fan of Brighton but it may b e a good idea to head to this town on the south coast today if in London. 9.39 or later train from London ( Victoria) is £22.70 return - less with a railcard. Return on any train. The journey takes about 1 hour. Unfortunately Brighton is not Tenby: > https://www.express.co.uk/travel/uk/1915085/Best-seaside-town-Britain-cobbled-streets-perfect-beaches
Anybody heading to the UK this summer should keep an eye on the weather forecasts & amend your activities accordingly.
PS. Anybody heading off to the coast should check that it is clear and sunny. This satellite view will also show up any sea fog.(Click with Radar to see where it is raining and the play arrow will show recent movement of weather. You can also click for temperatures). https://www.meteoblue.com/en/country/weather/satellite/united-kingdom_united-kingdom_2635167