Hi @stilldesign
I’ve had a look around this topic to try and advise the best I can (I’m not an accountant). An invoice displaying an ‘EU’ VAT number is for a non-EU based business but is required to charge VAT under the MOSS rules.
This guide may help:
http://community.quickfile.co.uk/t/what-is-vat-moss/8919
But your accountant would be the best one to advise on this as they would know the situation and your business.