I've mixed views tbh, but if pressed, then I think they should be compelled to honour the terms advertised.
At one level, we all make a mistake from time to time, and the odd mistake should be excused.
That said, TV adverts are not like a live broadcast, there's time to review and edit a TV advert, before it's broadcast, so in the case of a TV advert, I think they should have to honour it.
Mind you, I'd have a similar opinion of it were a sign in the window, offering goods at a certain price, but we all know that doesn't compel a retailer to sell at the price advertised...