I'm a bit surprised by some of these replies. Surely an NQT doesn't need a salary top up? Or a £2-300 top up to someone in a good job? I think it does young adults a lot of good to learn to budget.
DD1 is in her first job in Manchester. She pays £400 for her rent and bills, (small room in half decent flat), puts £100 or so petrol in her car and allows herself £600 for everything else, which tends to boil down to £30 for food, £60 for going out and £60 to splurge. She saves the rest of her salary.
DS1 is in a grad job in London on £27k. He pays a whopping £770 for his rent and bills, (again small room, half decent house). I know he budgets carefully and struggles to save.
Neither would dream of taking an allowance off us.