For VAT purposes, if a client is in another EU state, you zero-rate the services if they are in business and this is usually proven by looking at the VAT registration. However, if the client is below the VAT threshold or are not VAT registered for some other reason, HMRC says:
“If a customer claims to be in business but not to be VAT registered then alternative evidence should be obtained. This can be in the form of other reasonable commercial evidence or records that should normally be available, for example, contracts, business letterheads, a commercial website address, publicity material, certificates from fiscal authorities, and so on. A digital certificate from a reputable organization can also be used for this purpose.” [ https://www.gov.uk/hmrc-internal-manuals/vat-place-of-supply-services/va...
Does anyone know the EU VAT directive/legislation reference that deals with this? A client in France is not comfortable zero-rating the service for a business customer based in UK (who is not registered and is below the UK VAT threshold). They have asked for legislation references.