Post code look up in the UK with drupal

Post code look up in the UK with drupal

I've been searching for a Drupal solution (it could be Yii also) for post
code look up (UK only).
I've read loads of posts about that all points to private providers, Royal
Mail, etc however I've seen some pretty amazing stuff done with some open
source Drupal modules (location, layer, etc).
What I want to know is as of today, for my specific need (I'm creating a
very simple commerce/POS solution that needs to look up postcodes for a
local take away restaurant), do I need to buy some solution from a data
provider (postcodeanywhere.co.uk for instance) or I can achieve this with
Drupal's open source modules?
Thanks