Anything below £70k isn't worth consideration, unless you really want to be in London I guess. There will be better offers elsewhere.

Above £70k the range is basically £70k-100k, for a number of reasons. At £100k you end up in a different tax bracket, to the point where you may want to start considering taking other perks other than salary, to keep your tax cost down. Also, if you're being offered that kind of money, you're likely accepting a director-level offer, so really for engineers the meaningful range is about £70k-100k. Since you mentioned Palantir, I'll mention that I met with a recruiter of theirs who mentioned in our first (and only) meeting that their salaries were in this specific range.

For contract work, you can quite easily break the £100k barrier, but obviously now you're running your own shop with all of the issues that brings. Or possibilities, depending on your perspective!