I normally buy my National Lottery tickets by on-line subscription.
I can now no longer do this unless I give Camelot a DD mandate (which I will not do for reasons which are not part of this thread).
Now I know all about the economics of collection via DD and otherwise, but I will take some convincing that it is more economic for Camelot to ask my bank for £1 a week, albeit electronically, than it is to have up to £25 of my money in their interest earning account for up to 6 months at a time.
In addition, of course, I now buy at my local retailer, who gets to keep 5p of every ticket I buy.
You should always buy your lottery tickets from your local corner shop type retailer. As laurie53 says they get a percentage of it and it helps to keep them going. I've started buying most of my stuff from such a shop lately in preference to places like Tesco's and ASDA. Pity mine doesn't flog petrol?
I think the DD payments are required if you have a subscription ticket running and pay each week for the same ticket.
You used to be able to have this charged to your Switch card each week, but now Camelot have changed the T & Cs and require subscriptions to be paid by DD. This saves admin, and also means that Camelot are less likely to be penalised for returned payments made on stolen credit cards.