It's the whole world (or at least most of) and not just the UK.
Partly. It's mostly poor decision making. Those that thought it was a good idea to massively over hire during COVID (a likely temporary event) caused this. There was a surge in salaries across the board and huge confusion as teams tried to scale.
The hiring criteria dropped. A lot of people that otherwise wouldn't have made it got hired.
Many large companies today are still not yet down to below COVID levels in employees.