Possibly a Christmas TV show

Hi, this has been racking my brains all day. 

Looking for a UK TV show, maybe a one episode only, think it was shown around Christmas time a couple years ago...

Plot along the lines of a working family, where they put money aside as often as possible, and it goes in a tin in the cupboard. The daughter is after a dress possibly for prom, that they can't afford so the mum makes her daughter the dress. They also have their grandson living with them because their son is an addict, or in trouble with some people so is absent, however he does make a return in this episode. The money goes missing and they assume it was their son who stole it, but one of the family took it to buy a car for the daughter so that she could learn to drive, and one of the guys after the son I think is hit with this car...

I was thinking inside no 9, but checked all episodes and certain that's not it

Sorry it's vague