For promissory estoppel doctrine to apply, do you need a clear and unambiguous effect to the promise, either by words or by conduct?

Yes, for the doctrine of promissory estoppel to apply in English law, there must be a clear and unambiguous promise made by the promisor, either through words or conduct. The promise must be reasonably relied upon by the promisee, who must have suffered a detrimental change of position in reliance on the promise. The doctrine of promissory estoppel allows the promisee to enforce the promise as a binding obligation, even though the promise does not have all the elements of a formal contract. However, for promissory estoppel to apply, the promise must be clear and unambiguous, as well as capable of being relied upon, so that the promisee knows what is expected of them.