I only have the figures for end of 2018[1], but meta employed around 2300 people in the UK, if we assume the same distribution of jobs as elsewhere in the world about half will be engineers, so 1150 engineers. There aren't that many of these jobs. At goldman its a lot higher, aboutn 10,000[2] globally, but they only have around 3,300 employees in the Uk so if its the same ratio as global (25% tech), then that means around 800 developers. Again you'll note this is a very small number compared to the number of top graduates a year, with class sizes of 100-200 per university.
So like I said originally these jobs are few and far between. The point is that in the UK the salaries are much lower than those in the US and this is across all experience ranges.
