Take a look here:
http://www.theanswerbank.co.uk/Travel/Question 223554.html
If you check out the link which I've given there you'll see that there are fixed figures for compensation which must be paid if your flight is cancelled. If, however, your flight is only delayed (even though this might be by many hours), your only entitlement to financial compensation is a refund of the fare you paid for the flight (excluding taxes and charges). If you happen to be travelling on one of Ryanair's bargain flights, this could be less than a quid!
Chris