I have built an app specifically for UK shop owners for a people who regularly ships items to the UK, the app speeds up the checkout process as the customer only has to enter there postcode and then selects the correct address.
The main advantages of the app:
Speeds up the checkout.
Looks Professional.
Prevents addressing errors.
Saves money from returned items, due to addressing errors.
I will be putting a demo up soon, the app costs £50 and includes 12 months free access to the address database, after 12 months it cost £5 per 200 address requests.