I was in Sainsburys yesterday and spotted the new TTD range, exactly the same thoughts went through my head, £28.49 for 50cl works out at just under £40 for 70cl bottle! If I was spending around that in a supermarket I'd pick up the Lagavulin over a TTD islay. Perhaps they're hoping people don't notice its only 50cl, but surely those reading the label looking for 46% and non chill filtered will spot this.
Also using the example of TTD Islay, Laphroaig 10 or QC is usually available for a similar price so again why would someone pick a Sainsburys bottle over them?
Anyway they still had the old TTD range, so picked up one of them for under £20 to try