I just bought nearly 300 size 5 baby dry nappies for £33 because my store were able to process the order (online) for me for free in store delivery, and use my £5 parent club voucher which ends today 25th. In any case it would be 2x£18.99 for 3 boxes each with 99 in the box (it says 96 on the website but you get 99)
The voucher does say not for in-store orders and there is no online code on the voucher but looks like there is some discretion when you make the order in store, so worth a try!
I think this is the best deal available for these nappies (babydry) but if there is any better let me know. Otherwise I hope this helps someone