Double Vogayer; it'll have the formation A-(B)-C-D-FG-(H)-I-J-L (bracketed letters only present on 221s, not 220s).
A Virgin double Voyager, for reference, would be A-B-C-D-EG-H-J-K-L.
So it'll be wait on the platform around the end of the first 4 coaches and see which way round the formation is - something I've got used to with Tpex double unit services north of Preston!
Actually, each of the units could be either way round. I've been on sets which go A-C-D-F-L-J-I-G before (which along with the lack of corridor connections resulted in loads of people not being able to get to their reserved seats).