This is more of a research question than a technical question.
First I need to be able to draw sections of the uk like in this example : (http://blog.codebrain.co.uk/posts/uk_postcode_selector/postcode_selector.html)
Is there anywhere that has lat / long co-ordinates of the boundaries?
Following on from that is there a way to see if a postcode or lat/long position is withing these boundaries.
You can use geocoding for postal codes. And for sections you can use his kmz file: http://blog.codebrain.co.uk/posts/uk_postcode_selector/postcode_selector.kmz