Thanks for this.This is really helpful.
I have also looked into compensation for the 24 hour delay-which I think I am right in saying I am unlikely to get because it was a technical fault?

Re the downgrading,what if they said that was the only type of seat available on that flight at that time?

also i booked through an agent,major travel,is this relevant.I understand the regulations apply to the airline though.

edit-have just spoken to bmi cs .They are trying to say there is no other product exactly like premium economy-as could have been predicted.,ie telling me i cannot compare like for like. have quoted all this stuff and they have also tried to say it was the other carriers responsibility.I pointed out that is NOT the case.What do you think?.I have got a reference number from cs and have said i expect a response within 7 days as quoted in the regulations.I will then pe putting it in writing,quoting the failure to resolve in 7days.
I have stated that ,at the end of the day,whatever seats were or were not available,i did not get what i paid for.

Any opinions?