I’ve always found postcodes a bit vague and have preferred shapes like lower layer super output areas. The thing is, no one thinks in terms of the latter, especially those who should like the insurance industry, so we have just done a major upgrade to show visually on our maps – a close estimate – of where postcode districts and and sectors start and stop. Have a look at these pages and click on the relevant links to see what I mean;
Postcode areas – e.g. SW
Postcode districts – e.g. CR0
Postcode sectors – e.g. SS1 2