Watching Damned Designs on C4 and although the programme seems to be very empathetic towards them, I can't help but not feel particularly sympathetic for those people who have tried to exploit loopholes in order to build their houses without planning permission.
If you're not sure, go for pre-planning advice but for goodness sake don't skip planning all together!
Planning law is there for a reason, and that's not to satisfy the whims of individuals (btw I don't work in Planning, but have been through the process!)