This advice deals with the issues of consideration and promissory estoppel.
There are numerous definitions of consideration in legal texts, one being “‘A valuable consideration, in the sense of law, may consist either in some right, interest, profit or benefit accruing to the one party or some forbearance, detriment, loss or responsibility, given, suffered or undertaken by the other”.
In relation to Rent a Tents contract with Susie the terms of the contract are that in return for Rent a Tent providing a marquee for the birthday weekend Susie will pay £2,000. This is a binding contract as the several requirements to make a binding contract are, offer and acceptance, intention to create legal relations and consideration. ‘. However Rent a Tent then approached Susie and seeked to change the agreement and increase the cost of hire of the marquee to £2,500 to which Susie reluctantly agreed. Can this be considered economic duress? Lord Scarman stated "The classic case of duress is, however, not the lack of will to submit but the victim's intentional submission arising from the realisation that there is no other practical choice open to him."
It needs to be considered whether this is a new binding agreement and if the variation of the price is supported by sufficient consideration. ‘Sufficient’ does not mean that consideration needs to be adequate … ‘.The benefit or detriment need not be equivalent in value to that which is received in return…the point is that the benefit or detriment must be ‘legally sufficient’ in the sense that the law recognizes that benefit or detriment as constituting consideration, but its value is irrelevant. If both parties merely perform an existing contractual duty in return for a promise then consideration is not sufficient.
Here it would appear that Rent a Tent are merely performing their duty to provide a marquee and that Susie is paying extra for this so is not getting any benefit for the extra