If you go into a shop and they have a TV up for £20, you pay the £20 and carry it away then there is nothing the shop can do once they have taken payment.
Point is this isnt walking into a shop and buying it; in which case if the till assistant lets them walk off after paying so little they deserve to be sacked. Of course they are not going to chase you down the road and demand their TV back for your £20.
This is people ordering online, there is a world of difference. Trading Standards are not there to bully companies into giving out idiot prizes to people.
Anyone that thinks simply because they clicked the Checkout button that they the company is legally bound to them is sorely mistaken, and it tends to be the same people every time rearing their heads with consumer rights every time this comes up.