Daifly
You are the first person I have encountered since the EU directive came into force who appears to have had direct experience of a ramp check on a G-reg aircraft that involves a specific request for VAT documentation. Whilst Ramp Checks are common in France, they normally focus on Crew Licence(s), Certificate of Airworthiness, Certificate of Registration and any Maintenance and Insurance documentation that might be available. Many people carry VAT documentation in the same folder as these documents, but giving the ramp checker the opportunity to see VAT paperwork is obviously rather different to responding to a specific request.
Most such stories fall into the Urban Legend category, in that they always happened to "somebody I know", rather than directly to the reporter.
I am working on a project in this area and would appreciate the specifics of which aircraft, when and where if you feel comfortable letting me have the information. Drop me a PM.
2D