These salaries are terrible, how is it possible to get away paying such low salaries in London? In the US (not even San Francisco) I'd expect nothing less than 125k USD (105GDP)
PHP devs in the US generally get paid a lot less. 45-75k on the junior end and 80-105k on the senior end. I took a job in PHP/Wordpress/Salesforce because I liked the company and the people and I'm paid like half of what you said. In New York.
I can manage but yeah, I'm asking for more money soon. 125k as a baseline, especially in PHP, seems absurd to me. Sure, I could switch to any of the stacks that I'm more familiar with and make way more, but with a lot more hours and stress added.
I get my work done in ~30-33 hours, am not on call, have a lot of influence over our products and like absolutely everyone at the job. From my perspective, more pay seems like golden handcuffs. Here I am free to live my life.
Fun bit of trivia: the UK government spends less tax money on everyone's health per capita than the US government does (before you even add on health insurance)