I would probably spend, to feed 9 adults and 4dcs:
Arrival nibbles & drinks (nuts/crisps/beer/prosecco) - £15.
Ingredients for soup plus bread rolls - £10.
Turkey probably £50-70 depending on where from/size.
Pigs in blankets, stuffing, cranberry etc £25.(everyone likes lots).
Potatoes, carrots, parsnips, sprouts £10-15.
I get prosecco for around £8/bottle so maybe 5 of those.
Christmas pudding, ingredients for white sauce, profiteroles for those who don't like Christmas pudding - £12ish.
Crackers £10.
Boxes of chocs for snacking, cheese & biscuits, grapes etc £15-20 depending on cheese.
Probably £200 in total depending - you could get cheaper crackers, wine or prosecco deals etc and a cheaper turkey or smaller turkey crown which has less wasted bits. So you're not far off with £150 especially if someone brings a bottle or offers to bring pudding or nibbles etc.