This morning I had my first sea swim at Scarborough - no wetsuit, and RNLI on standby ( my son is a lifeguard ) . It lasted 15 minutes max, but you have to respect my "trusted" status as I have no photos to prove it !
The North Sea temperature right now is around 12 Centigrade, and it's not much more anywhere else on the UK coast ( 15 around Channel Islands ). In the Philippines it's 28, much the same as indoor pool temperatures here .
Sudden immersion in the sea off the UK, or our rivers / reservoirs can lead to cardiac arrest from immersion before there's time to drown . It all depends on age, general health ( and alcohol levels ) - I've survived to post this news .