Tesco Value Joke

So I was in the supermarket the other day, looking at the ready meals, when I noticed that instead of price stickers, all of them just had a letter-number sticker on them, which either read just "D1" or "D2". That's odd, I thought, so I grabbed a passing shelf stacker, and asked him:

"Mr O'Brian," - because I'm polite you see, and I read his name off his badge - "I wonder if you might explain what these stickers mean?"

"Well," he replied, "Everything marked with a D1 is on very special offer. Basically it's all the stuff that's nearing its sell-by date, so really, we're either going to flog it on really cheap or just chuck it away. And call me Kenneth."

"Oh, OK," I said. "So how much would it be then?"

"Well, like I said, we'd only be throwing it away anyway, so it's just three pence."

"Wow! That's great. But what about the rest of the stuff?"

"That's the thing, you see, because if it's marked D2, then it's just normal price."

"Right, I see."

So, always one for a bargain, I grabbed two packs of microwave ravioli, two of lamb korma, and two of prawn noodles.

It's all good I think, as the woman on the check-out beep beep beeps it all through, but then...

"That'll be £4.10," she says.

Wait, that's not right, I think.

"Look," I said, pointing at the labels, before realising my mistake:

"See? 3p! Oh... Are two D2? Oh, be 1! Ken O'B, you're my only hope!"