I keep a spreadsheet, so I know exactly :)
This year it was £350 each on my two. However, this includes some things which, although they are wanted presents, are also things we'd typically chip in with - i.e. new expensive sports equipment, or musical instrument related items. Also stuff like new PJ/slippers , branded clothes etc in there, which are practical items that we'd probably replace throughout the year if not given at Christmas (but would perhaps not be branded if not given as a gift).
It varies year to year, depending on their wants and needs. It generally seems to go up rather than down, though! Hopefully it will stay at this level now. Pre-teen ages, it was more like £150 - £200 ish.
TBH, everyone's budget is different, and everyone has different ideas of what to give for Christmas, so you can't really compare with others. As long as your DDs like what they are getting, and you can afford it without getting into debt (or causing yourself undue stress) then its all good .