P threatened to sue D on a criminal offence if D did not pay for his son’s liabilities where the son had forged D’s signature on a recommendation note. Therefore D agreed to pay his son’s liability but later claimed that the agreement was invalid due to undue influence. HL held that this was the case and supported D.
Lord Westbury: If a man agrees to guarantee another’s liabilities he has to do so as a “free and voluntary agent”. This is not the case where a man’s refusal to enter such a contract will lead to his son’s criminal conviction.