The restrictions on cabin baggage prohibit "pointed or bladed articles capable of causing injury". This description would seem to include both knitting needles and crochet hooks but I've never heard of anyone being refused permission to carry any form of pen: http://www.ryanair.com/site/EN/faqs.php?sect=b ag&quest=prohibiteditems
Chris... your phrase "the rules are common to all airlines" is not strictly accurate.
Although true of the UK and many other countries, for flights originating in the US there is not necessarily any prohibition of "Guns, firearms, ammunition and weapons (including replica items)" as checked-in baggage, therefore nationality (or perhaps that should be geography) is a factor.
Airline /airport security is a joke and a knee-jerk reaction to some perceived but unsubstantiated threat since 9/11. I was allowed to carry my own personal pocket knife.....a lock-knife with a 4" long pointed blade....to Ibiza and back aftering offering no more than an apology for not leaving it at home. I'm not a kid and have carried a pocket knife as a useful tool for decades with no problems. Hysteria rules.