You can do bulk buy on amazon which is cheaper. You can only get discounts on 6 month plus formula, though, it's not allowed to discount infant formula from birth so you won't find any offers on that. But definitely on nappies.
Apparently Tesco have a baby event starting 14th Jan other supermarkets tend to join in and have them on the same time ish. Aldi nappies and wipes are good and cheaper than special offers in other supermarkets.