(I'm particularly experienced (15 years) in Python/Django, JS/Vue, UI/UX)
At this rate, I was slightly outside of the normal range at lots of places. It helps if there is a Managing Director that knows you're decent as they can help to sign-off on higher rates. Unfortunately I found this almost impossible to regularly achieve because it takes time to build your network and show your worth. Having to constantly start again with zero reputation at every workplace I go to was one of the reasons I decided to stop contracting. The other reason was the downturn in the contractor market caused by the possibility of IR35 enforcement and the reaction to this by big risk-adverse companies.
You are right though, that it was getting more and more difficult around then. At the first firm they stopped granting outside IR35 contracts during 2020, but were able to grant extensions if one was requested by somebody in leadership however eventually the extensions themselves were only allowed to be one week at a time so I left.
I've actually stopped billing myself as a fullstack developer for contract work. Increasingly the companies which use contractors will be looking for front end or backend roles only.
The market has been taking a hit recently with all the uncertainty combined with the usual slowdown over the summer season so if you're looking today and you want a quick start then you might have to settle for less. But schools go back next week and everyone is back to work after holidays so then we'll find out how much of the drag has just been the usual seasonal slowness and how much might be with us for longer.
My experience matches everyone else in this sub-thread, £650/day for years and finally reached £700/day. But as these are short term projects it averages to less. For 15 years experience it's not great.
I don't have the option to move to the US but I'd like to pick up US clients remotely. It's the only way I see to earn more.
We've (small UK development/consultancy shop) occasionally had US-based clients approach us about small projects. It's not something we'd actively explored until recently because of the potential legal and accounting complications. When we did finally look it turns out it's probably not so difficult after all though we haven't actually tried it for real yet.
The rates that small outsourcing firms or individual contractors charge in the US are so much higher than the UK that a US client could get a bargain working with us while we could be charging much higher rates than we get from UK or European clients. Financially it's a situation where everyone could do well.
I'm a bit surprised that we don't see more trans-Atlantic deals. Maybe a lack of awareness or concern around time zones means people don't really consider it an option? But even California is only an 8 hour gap so with almost everything being primarily remote and async today it should be possible to communicate effectively.
You can obviously expect more premium £700-£1,000 day rates if you're working for banks or big four accounting firms, or if you have very specific or highly demanded skills (e.g. React)
Probably very varied by geo / industry as well - from my experience as a permie 50 miles distance or working for one type of bank instead of another can do multiples on your salary.