As a counter point in London, I've found supply to be pretty good.

Multiple actually good and talented candidates to basically pick the best from, and not just dregs with "this person will do I guess - 50% is better than nothing" type sentiment.

Supply in London is fine, companies just need to raise their salaries tbh.

I personally moved companies during covid and got a more flexible role and a 90% increase.

Recruiters are going nuts on LinkedIn atm for anyone with skills and the salaries are rising from there.

I've turned down job offers in London because I can get the same salary with a 33% reduction in cost of living elsewhere or work in London for 200% of the salary doing software engineering for finance.

With IR35 reform in full swing, I'd expect quality supply to incease as contractors start to seek full time positions.