Phil, as no-one better qualified has replied here is my pennyworth! Ortolan would be a very rare bird at this time of year and rare birds are usually only seen singly!
If you saw a pair(or two) then they are more likely to be one of 'our' birds. Light is all important as is distance, angle,optics used,call note and behaviour. You really need to buy a modern field guide(Collins guide by Lars Svensson and Killian Mullarney is the current bible) and get a digital camera for such a moment! Our local Ceredigion Bird Report is a good guide to what is most likely to be seen and Jon Green's Birds in Wales also presents the scene historically.
Strange things can happen however so that is where the digital camera comes in (or very detailed field sketches) and a mobile phone to alert a nearby bird expert.
As this blog is about sightings: GOSHAWK carrying food,mobbed by jackdaws at Abermeurig today, really low overhead, nearly caused a RTA!