The regulations are there but, certainly in the UK, they are pretty meaningless and the airlines regularly flout them - some are worse than others. If you know your rights you can insist but when they do not comply you are left with court as the only recourse. KLM blatantly refused me boarding onto a connecting flight at Amsterdam when they were still accepting other passengers. Over the course of time they gave three different reasons for this on three different occasions, the last one being in effect that "the computer said no". The UK watchdog gave up and said I could go to court - there are EUR600 at stake, according to the rules. All those put into this position should know that they are entitled to hard cash and are advised never to accept any vouchers or anything else such as "a gift" (which I was offered).