If you have a look at the dates already announced for the UK, see if they have a few days off either side. Usually, when tickets are announced for big acts, they have usually provisionally booked the venue for more dates too, but they just don't announce them for a while incase the ones already on sale aren't likely to sell out. For One Direction though, aren't they doing 6 or 7 nights at The 02 in London? I doubt they'll announce more than that if they are.