Managed to grab a very cheap pair of scarpa touring boots online - worth the punt even if I had to re-sell them, but I'm struggling to know if they're too big or not.
I'm a UK9 foot, typically wear 27.5 Salomon alpine boots with my toes rammed pretty far into the shell. I ordered these based upon a "UK9" sizing, but they have arrived with a 28.5 liner.
These, with the liners out, have about 17-19mm behind my heel (measured by putting a felt tip marker in) with a bare foot and big toe against the front.
With the boots on and tight, and my own insoles in, I have a little heel lift and can wiggle my toes even when standing upright (i.e. not locked down and toes forward). The mid-foot feels good, but I would have certainly asked for a smaller size if they were alpine.