Yeah, I have the misfortune of being a chartered town planner.... However for PD rights I must confess I normally use
http://www.planningportal.gov.uk/permission/ to navigate the process? Side extensions tend to depend on where you live and distance to boundaries etc.
One thing to check is that your PD rights haven't been removed by the council in some way, are you in a Conservation Area or is it a reasonably new house?
