I've followed this thread (as needed to buy a carseat, but got a Britax one, still reduced by 50% though in Mothercare!).
I'm really surprised people are so hacked off they're talking about not shopping there again. Tbh, if I made a mistake financially in that way, I'd really hope people could understand the mistake and let it be rectified, rather than saying "by law I am ENTITLED to this, so you must lose loads of money".
And hopefully no-one has LOST anything, just disappointment that it really was too good to be true...