If your flight is delayed at departure, you have the right to assistance, to reimbursement and a return flight, depending on the duration of the delay and the distance of the flight....
Damn EU forcing these rights on UK consumers against their will.
If you are downgraded, you are entitled to reimbursement of a percentage of the price of your ticket, depending on the flight distance as follows:
a) 30% - flights of 1 500 km or less
c) 75% - flights not falling under (a) or (b), including flights between the EU and French overseas departments.