Help with what clothes to pack for UK visit

[GirlInTheDryShirt]

We live in the south of Spain where it’s currently about the same temperature as the surface of the sun and we (DC10 and I) are off to London tomorrow for a four day trip. I’m terrible at judging actual temperature by the weather forecast since 20°C feels chilly but in the UK definitely feels warmer (maybe the humidity?)
Anyway, should I pack shorts for DC or is it jeans, trainers and jumper weather? Do I need a big coat or is a thin mac sufficient? Thank you in advance to anyone kind enough to give me a steer!

My weather app says its going to be 26 degrees in London this week but raining on Thursday.

Definitely not jumper weather for me. I'd prob bring jeans AND shorts, t shirts and a thin coat for the rain. Maybe travel in the jeans to save space?

It's 22C here today.
I'm in jeans.
DS (12) is in shorts.
DH is in shorts, shirt and tie 🙄

You might like a thin jumper for the evening, since you are used to sun-like temperatures.

Yes to a thin, waterproof, coat.
Probably yes to trousers (although see what DS would prefer - mine would always choose shorts unless it was freezing).