There is no problem driving a foreign (I assume probably European) vehicle in this country, as long as it meets all the vehicle requirements of its native country. This is what you should get proof of. This is of course your problem; paperwork varies between countries. When I used to drive my artic truck to Austria and thus through Germany, I was quite often asked for the trailer registration document by German police(as required by German law). However, in the UK there is no trailer registration, so us UK drivers didn't have the paperwork, but try convincing a copper in pidgeon german at 3 o'clock in the morning of that!! If you are unsure, probably best to refuse, but technically, if all is in order there should be no problem.