P sold assets to D. D was to pay back installments. Payments were late a lot, but P still accepted them. Falling out between P and D. Ds payment was 36 days late. P demanded entire sum
For estoppel to apply, ones conduct must amount to a promise or assurance, intended to affect the legal relations of the parties.
The equitable defence in Hightrees cannot be invoked unless there is some evidence that one of the parties entered into a course of negotiation which had the effect of leading the other to suppose that the strict rights under the contract would not be enforced.
Parties did not enter in to negotiations that would have had the affect of leading D to believe that P had agreed to disregard that part of the contract.
No promise that intended to be binding here – D liable for entire sum