I would negotiate with the parents, tell them to give you £4,500, let you buy a car a year or two older that is larger such as an Astra (not a Focus as they are relatively desirable/expensive) which will be more confortable, safer and better equipped. It could also be easier to sell later as a supermini with 80,000 miles will be less sellable than a medium sized car where 80,000 is average.
You can then tell the parents to stick the spare £1500 in a savings account, then in 24 months when your excellent choice of car is still running sweet, they can go and enjoy the cash themselves or give it to you as a reward for not buying a lemon 
(plus, many aftermarket car warranties are not worth the paper they are written on. Mine was void before I walked out of the dealership as the second service had been done a tad over 10% late (i.e. service due at 10,000, records show it was done at 11,200) and didn't cover stuff like "any electrical issues".
My gf does a 60 mile round commute and she has recently commented that the seats in our Ford Fusion are a bit hard. (Not surprising as we had the luxury of a Mondeo TDCi a year ago, lovely car. In the months between the Fusion and the Mondeo we had a Punto and both hated the thing with a passion. If you do look at a Focus, the equivalent Mondeo is usually the same sort of price but comes with loads more toys)
