Quoting the dissenting judgment of Lord Sumption in Patel v Mirza [2016] UKSC 42 (at para.226): “The common law is not an uninhabited island on which judges are at liberty to plant whatever suits their personal tastes. It is a body of instincts and principles which, barring some radical change in the values of our society, is developed organically, building on what was there before.” Sometimes, the common law develops slowly. An example of this can be found in Boult v Together Personal Finance [2026] EWHC 809 (Ch), in which Green J considered the scope of the 400-year-old rule in Pigot’s Case (the “Rule”).

The Rule

In 1614, the court determined a claim brought by Benedict Winchcombe against Henry Pigot. Winchcombe relied on a deed pursuant to which he had advanced a loan to Pigot. Some time after the deed was executed, a third party had amended the deed to insert that Winchcombe had become the High Sheriff of Oxfordshire (which was, at the time of alteration, correct). When it came to repayment, Pigot sought to invalidate the agreement, arguing non est factum (this is not my deed). In what became the Rule, the court confirmed that a material alteration to a deed or other instrument after execution by one party, without the knowledge or consent of the other, renders it void. As the alteration in question was not material, Pigot did not succeed in defending the claim against him.

The Rule developed over time and has become a well-established part of English law. In Raiffeisen Zentralbank Osterreich AG v Crossseas Shipping Ltd [2000] 1 WLR 1135, the Court of Appeal reaffirmed the Rule, which they acknowledged to consist of two elements: (1) The alteration must have been made deliberately; and (2) The alteration must have been material, namely there has been some alteration in the rights and obligations of the parties.

Facts of Boult

Ms Boult sought a loan from Together Personal Finance (TPL) to repay her existing borrowing. Ms Boult intended to repay the loan with the proceeds of sale of her home. Ms Boult agreed only to charge her home by way of security. After Ms Boult signed the legal charge, TPL’s solicitor added by hand the title number of a field she owned. This addition was made in the mistaken belief that Ms Boult had agreed to include the field and her home as security for the loan.

Ms Boult failed to repay the loan within the term. Eventually, TPL issued possession proceedings against Ms Boult in relation to her home (but not the field). Ms Boult relied on the Rule, arguing that, due to the alteration of the deed, it was void. The questions for Green J were: (1) does the Rule apply where the alteration was intentional but made under a mistaken belief? and (2) was the alteration material?

Rule applies when the alteration is deliberate

Green J noted that if a deed of the type under consideration could be amended without the obligee’s consent, this would open the door to the type of fraudulent conduct that the Rule was designed to prevent. The simple fact was that this was a deliberate alteration designed to affect the rights and obligations of the parties. It did not matter that the alteration may have been the result of an innocent mistake. It was deliberate and that was what mattered.

Time when materiality is assessed

TPL argued that Ms Boult had not been prejudiced because it had not sought possession of the field. Green J underlined that, at the time the deed had been altered, there was clearly potential prejudice to Ms Boult. The alteration was material when made, so the deed became void from that moment.

Conclusion

It should go without saying that one should not seek to alter an agreement after it has been signed without the consent of the parties to that agreement. Further, to avoid a party raising the Rule in order to avoid enforcement of an agreement, any alterations should be signed or initialled by the parties to avoid later disputes as to whether the alterations were in fact agreed.