Ps had a contract of lease on a house which they had the option to renew. However D claimed that the option was void because the houses weren’t registered under the land registration act. Oliver J said the correct approach to any estoppel is by “ascertaining whether, in particular individual circumstances, it would be unconscionable for a party to be permitted to deny that which, knowingly, or unknowingly, he has allowed or encouraged another to assume to his detriment”. Because of the circumstances in each case, he said that one P could rely on estoppel, whereas the other P could not.