Ah the old style focus is notorius for this!! I have the new style one and they've extended the belts just enough. You can get seat belt extenders just like you would in an aeroplane, or you can have the whole seatbelt replaced (a bit pricey). I would have considered the seat belt extenders although they are not 'made or approved' for use with car seats, but they are made to secure 'larger' people! When I asked about this at the shop where I bought mine the guy said the silvercross one is actually one of the better ones for fit in the focus, it really is a ford problem, sorry!