Sorry, no beginning of a definite answer - but I can't help wondering why you didn't ask in Ostend. Either call the airport operator directly - the number is in the AIP - or I should think the nice people at NZVC would be glad to offer advice.
That said, the Brits have decided to let Europe's best wonder pass them by, for good or for bad. And I do recall that, as a Belgian citizen, I found British entry control more than satisfied with my simple identity card. But then, do I recall there is no such thing as in identity card in the UK, so it has to be either a full-blown passport or secondary proof like a driver's or pilot's license?