Without thinking about it too much, I'd say it boils down to when there has been a meeting of the minds and I think it does somewhat depend on the actual price paid and the availability of information
In any typical bar situation, the performance of the contract is often carried out before a price is actually known, on the reasonable assumption that there has been a meeting of the minds ("I want X and will pay the price you are charging for it"), and together with the fact that prices are available if requested it seems obvious the contract has been made at the point of order.
In the OPs example, there has effectively been a representation as to what the price of the second round would be on the basis of the first round. The availability of the info regarding the promotion would be the deciding factor here, I think, with some emphasis on price. If there is truly no information regarding the expiry of the offer, with the price of the first round taken into account, it would seem perverse to say there had been a meeting of the minds, particularly if the price is dramatically different. Also, the rule of thumb is that terms of a contract are generally construed against those that are trying to enforce them, to promote certainty, so it would for the bar to evidence that it's reasonable to insist on the higher price (again, which will depend on availability of info and the price difference).
Taking it to an extreme example, if you ordered a standard spec boat that anyone could order, but it was built specifically based of that order, it would seem perverse to expect the buyer to pay any price (i.e. A £££ price) revealed to the buyer upon delivery of the boat. "You could have enquirerd about the price" falls apart.
As a further example of a false representation, see the first six words of this post
In any typical bar situation, the performance of the contract is often carried out before a price is actually known, on the reasonable assumption that there has been a meeting of the minds ("I want X and will pay the price you are charging for it"), and together with the fact that prices are available if requested it seems obvious the contract has been made at the point of order.
In the OPs example, there has effectively been a representation as to what the price of the second round would be on the basis of the first round. The availability of the info regarding the promotion would be the deciding factor here, I think, with some emphasis on price. If there is truly no information regarding the expiry of the offer, with the price of the first round taken into account, it would seem perverse to say there had been a meeting of the minds, particularly if the price is dramatically different. Also, the rule of thumb is that terms of a contract are generally construed against those that are trying to enforce them, to promote certainty, so it would for the bar to evidence that it's reasonable to insist on the higher price (again, which will depend on availability of info and the price difference).
Taking it to an extreme example, if you ordered a standard spec boat that anyone could order, but it was built specifically based of that order, it would seem perverse to expect the buyer to pay any price (i.e. A £££ price) revealed to the buyer upon delivery of the boat. "You could have enquirerd about the price" falls apart.
As a further example of a false representation, see the first six words of this post
