Many thanks for the replies concerning the seating plan.
The flights were Sunday 2nd August (outbound from Manchester) and Wednesday 12th August (inbound to Birmingham) I have just checked and indeed the outbound flight from Manchester is showing a wide body (A330 ??) seating plan. I never thought of this possibility as I thought that the A330's were leaving the fleet ?
I know that the A330 operated the Sunday flight on this route last year, but it seems a bit of a recipe for chaos if the plan has not been updated and people are being allowed to book onto seats that will not even exist when they turn up at the airport.
Maybe the A330 is being given a stay of execution ?