I’m not sure, Duke.
Legally, displaying goods with a price ticket is what’s known as an ‘invitation to treat’. The sale contract isn’t finalised (in a shop) until the ‘ringing of the cash register’- the acceptance by the cashier if the money you proffer. (It came from a case brought by the Pharmaceutical Society of Great Britain (against Boots) who were hoping to secure more jobs for their members, as the law said a pharmacist had to be present at the sale of some medicines, so there had to be a definition of exactly when the sale occurred).
It might’ve been different before that case, (which was I think, from memory, in the 60’s).
I think a number of online retailers pushed this, just as the internet caught on, and fir online shopping there’s now a distinction between an order being placed (which is analogous to the ‘invitation to treat’), and the order being accepted - which is when the contract is finalised, the price fixed (and usually the payment is taken).
Unless you’re IW, in which case the price is what Peter says it is (but he might only tell you a quarter of the true price, which is how he often seems to work the flexi-pay scam…)