Hello my name is ***** ***** I will help you wtih this.
The price on something is just as you say, an invitation to treat.
It is the recommended retail price, not the actual retail price.
Therefore it is an invitation to treat because the contract can be cancelled up until you pay the money.
So you can take the item, walk around the shop and put it back.
If that was the point of contract as soon as it was picked up you could not change your mind.
When you take it to the till and the person says, that will be £1 please, as soon as you hand over the £1 that is the point of contract.
This is because even at the till you can change your mind
Once you hand over the £1 that is the contract
So if the thing has an RRP of £1 and the till says £1.50 - it is £1.50. You can change your mind
The case you want is: Pharmaceutical Society of Great Britain v Boots Cash Chemists (Southern) Ltd  EWCA Civ 6
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