To cut a long story short we went out with part of the family over Christmas and we had to leave early. DP paid our part of the bill and left another £70 with my step mum which he said should be taken off the bill before it was divided - basically it was £10 per person off their bill so not a huge amount per person but worth having.
I've just spoken to my sister who says this was never mentioned and the bill was divided up to the penny. She knew nothing at all about the extra money DP left. I haven't told him yet but know he'll be hurt as he meant it as a small gesture to them all for Christmas