The contract market in London is in a difficult place at the moment. IR35 has generally made buyers weary (in a way they weren't before) as well as limited the type of work contractors are given; budgets have also been very tightly squeezed because of Corona, it's hitting contractors pretty hard.

As a 'buyer' of these services myself, full-stack JS dev contractors are in one of the most oversaturated parts of the market and many in my network are attempting to find full-time work at the moment. Those that aren't are having to compete on rates in a way they never have before, definitely a buyers market.

The other side of this is how much more volatile contractor work is than before, many companies with a mixed full-time/contractor team see their contractor pool as the most 'expendable' when cuts need to be made. Many people in my network have had existing long-term contracts ended with little to no notice.

I've also seen limited evidence the pushing back of IR35 to next year is changing the policies towards contractors at large corporates, where (by volume) most contractors get their contracts.

In short, I don't think it's the best time, but: if you do make the jump, make sure you have contracts SIGNED before you make any big decisions. Not a hand-shake or an email, a written contract. If you can get that, then you'll be in a good place.