I was due to travel from ATH-LHR in CE yesterday at 20:45. At around 11:00 I got a text message telling me that the flight was cancelled when I was already en route to ATH.

This was followed by an email telling me that I was rebooked on a later flight but in ET. I checked for CE/business availability on this and other flights (including Aegean) but there was none, so I had no option but to accept.

BA is now insisting that the downgrade is voluntary because I accepted the rebooking. I don't see that I had any option and want to claim under E261. I think BA is wrong, but I'd appreciate advice please.