I said I would only explain this once, but some people clearly weren't listening, so I am going to have to say it again. But differently, because this time it's for the slow people.
I saw a sign in Carter's on Saturday (I should explain that I was not in Carter's, but going past on the bus; I should also explain that yes, I was in Belfast city centre on the Saturday before Christmas, and that I left quite quickly) which said that they are offering VAT-free prices (or some such; I forget the exact phrasing), by reducing prices by 15%.
But of course this is incorrect, and I shall now explain why.
Suppose that pre-sale, an item cost £100 (this is at the new, lower, rate of VAT).
Now, if they reduce it by 15%, the new price will be:
(£100*85)/100 = £85
However, if they merely removed the 15% VAT, then the new price would be:
(£100*100)/115 = £86.96
which is not so good, so you wonder why they make that claim.