yep its the law. Still though if it keeps happening then...
But that's not at all what happened in this case.
As has already been mentioned, a shop sticking a price tag on an item is not legally binding - goods that are displayed, whether that be in a catalogue, on a shelf, in a shop window or on an internet site, are only there to entice the punters to make an offer to purchase said items. Hence the term "invitation to treat".
The argument that the indicated price must always be adhered to is often quoted but is incorrect. A retailer/vendor is legally entitled to refuse to sell you a particular product if he so wishes - and that includes if he becomes aware that an item has been incorrectly priced.
The only exception to this would be when a retailer explicitly and continually advertises an item at a certain price yet doesn't honour the price despite being made aware that he has incorrectly advertised it. However, it would have to be proven that the retailer was made aware on numerous occasions that the advertised price was incorrect and he purposefully ignored amending the price.
The famous cases pertaining to the practice of "invitation to treat" that everyone learns about in A Level law are the Boots one, whereby it was determined that picking medicines off the shelf and putting them in your basket didn't equate to a contract being formed to sell you the drugs - that only happened when you got to the checkout and the checkout girl either sold you the medicine or didn't; and Fisher versus Bell, whereby a copper tried to argue that the flick knife that was on display in a shop window contravened the Offensive Weapons Act (think that's the right Act... was a long time ago that I studied law), but the defendant said it was just an invitation to treat and if anyone had tried to buy it then he would have refused cause it was against the law - the judges agreed with him, and now all law students learn about this case
What you're referring to, when talking about "bait and switch", is something different, and protection for the consumer, in this case, would not be offered under the SoGA. I'm not actually sure if there actually is any protection to anyone who finds themselves in this situation... after all, places like DFS or Land of Leather seem to get away with this practice every time they have a sale on (and that's pretty much all throughout the year!)