I still do not understand. your policy should cover you in the policy territories, which should include the EU and you should have minimum cover there. They should give a better reason, than a simple NO.
The Driving of Other cars extension from hibernian applied when i was in france some years ago. I telephoned before I went, got a friend's car over there and drove on the hibernian policy.
are you through a broker or direct. if direct, ask to speak to someone in control, such as the person who signed the cerificate or the head of motor business.