Thanks everyone.
A couple more questions regarding baggage. My wife and son are each intending to carry rucksacks on board which are obviously irregular, soft and tend to bulge with the contents. Are these things actually measured or do they just have to fit inside a frame of the airline's predetermined dimensions? I know the answer to this ought to be common sense but, after what I've read about Ryanair, nothing would surprise me and I have visions of some jobsworth with a measuring tape trying to find a dimnension which exceeds the limit and thereby extort money.....
Also, if it's all self check in etc., how and where do they label/tag and drop their checked in luggage bags for the flight?