What's the correct country code/prefix for a UK unique taxpayer reference I should give in an invoice when supplying services overseas? I suppose it's simply UK, but I couldn't find anything about it on the Net. I found some articles regarding tax numbers in other countries, and they for example say that in Poland you should add PL before a tax number, that's why I suppose it'll be "UK" in the UK, so:
UK 1234567890
Am I right?