Best answer by Phil_H
It sounds like a difficult situation. I am not sure a meter reader would have any more luck than you would in accessing the meter. Is there someone/caretaker on-site who has access?
Have you spoken to your local Citizens Advice? See:-
They can probably give you some good advice and they will be local to you and will know contacts at your council.
Also in this situation I would contact Ovo directly by phone to discuss this with them. As they "own" the meter they do require access. I suggest you have the contact details of the key holder/person at the council who you contact about this ready to give to Ovo. If you have been unable to provide meter readings for 2 years Ovo should be insisting on access.
Ovo would need access in any case if you want a smart meter fitted.