Principally we supply goods and services out of the UK and hence our first point of reference is UK rules and regulations which stem from the EU VAT Directive.
What these state is invoices under the value of £250 can use 'simplified' rules, and it's these rules we use in creating our invoices, you can read at the bottom of this article here: http://ec.europa.eu/taxation_customs/business/vat/eu-vat-rules-topic/vat-invoicing-rules_en#what_information
This Simplified mechanism stems from the EU VAT Directive here: http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32001L0115&from=en if you search for "Simplified" in this document you'll find the relevant section.
Some customers have asked us about inclusion of additional details in our invoices (usually their address and/or their VAT number), but as long as your invoice from us is under £250 then we'd suggest following up with your own VAT regulator to confirm their agreement with you claiming VAT appropriately based on the above directives.