Really depends on what you do: our last house/kitchen (albeit directly before covid so miles cheaper) we spent £15k and that covered the room totally gutted, old concrete floor dug out, new joists and subfloor, engineered wood, worktops, lighting, plaster, some roof repairs, back door, kitchen door and some other stuff I can’t recall; new layout so plumbing and electrics changed too. Kitchen itself including appliances was cheap from IKEA and we got it on 0% loan to stretch our reno budget further.
If it’s just changing carcasses, appliances and worktop but not touching the room itself beyond a paint refresh that’s miles cheaper. But prices for labour and materials on things like plaster, electrics, joinery, etc, have soared in the past five years.
If it’s a house in good working order, £20k is fine, though not generous, to do some bits. If it’s a creaky money pit like all of mine seem to be… Basically don’t go in planning to do big work with £20k! Anything you do in an old house uncovers some DIY fuckery that has to be undone.