Ok bit of a story with this one.
My local Morrisons had Halo Reach branded 12 months + 2 free for £17.99.
As they were display cases they had no barcode, so the girl at the checkout called for the assistant at the bit they keep the dvd/games etc.
The girl brought over 2100 Halo Reach branded points and scanned them, they came up at £17.99.
I told her MS points was not the same thing, so she brought over a CURRENT live sub that scanned at £34.99.
Now 2x£17.99 should have been £35.98.
In the end she ended up letting me have the 2 subs for £34.99!!
Prob store specific, but DEF worth checking!