I may have been a bit premature on saying it works ‘perfectly’ although in theory it does. Basically it works for the PO postcodes but it errors with the SO postcodes. Strange!
I’ve posted another question on this to see if it’s an obvious error we’re missing. I’ll copy the link in case you have a spare moment to take a look. I don’t really get why it errors on the SO, it’s like they’re even not in the code.