Let's say someone twisted your arm into voting a particular way, entering a contract against your will or giving them a substantial gift. Fortunately, there are protections in the law against "undue influence" to stop people from being improperly pressured into making legally significant decisions.

The principle comes under a branch of law called “constructive fraud”. It covers trickiness that the courts construe as being fraud even if the culprit was not engaged in outright deception. It is enough that someone is pressured to do something with a legal consequence while not exercising free and independent judgment. For example, under the Representation of the People Act 1983 it is a “corrupt practice” to exercise undue influence over a voter. (In fact, the phrase “undue influence” was popularised after being coined by Henry Bolingbroke in 1735 in an essay about improper electoral practices.)

Today, most of the law in this area concerns contracts and gifts. In one recent case, Goodchild v Branbury, Leslie Goodchild, a frail 77-year-old man, gave a valuable one-acre plot of land to his great nephew, Shane Branbury. But after Mr Goodchild died, the gift was successfully challenged by lawyers as having been made after “undue influence”. It could not be explained on the basis of Mr Goodchild’s relationship with his great nephew and he made it without taking any legal advice, so the gift was held by the Court of Appeal to be invalid.

In certain set relationships there is, in the nature of things, an imbalance of power and knowledge, such as that of bank and customer. These relationships can be seen in law as being such that if the "weaker" or dependent party makes a substantial gift to the dominant party, or a personal contract with him, it will be presumed to be invalid. This is called a “presumption of undue influence”. The only way the more dominant party can persuade the court that the gift or contract is okay is by showing that the other side took independent legal advice before going ahead.

These days the relationship of husband and wife is a fairly balanced business. But there is still some law to stop a dominant partner from bullying the other into making an unfair gift or agreement. The relationship of husband and wife doesn’t automatically raise the presumption of undue influence, but it can be argued in any particular case. The law’s analysis of marriage can at times seem cynical, but it is only so in a technical sense. “A large gift by a wife to her husband will be regarded with some degree of suspicion,” according to one major legal text, however it goes on to note that the transaction will be set aside only if there is proof that the wife was unduly influenced to make the gift.

The solicitor-client relationship automatically raises the presumption of undue influence. A solicitor cannot take a gift from his client unless he can prove that the gift was entirely uninfluenced by the relationship. Equally, a purchase by a solicitor from his client will be set aside unless it is shown to be manifestly fair. The confidential relationship of barrister towards his client is similarly controlled.

Lawyers have sometimes been depicted manipulating their clients’ wishes in worse ways, although thankfully such activity is very rare. When Lionel Hutz, the attorney of dubious ethics in The Simpsons, is appointed executor of Marge Simpson's mother's estate, he gathers her family near a television. “She left a video will so I earn my fee simply by pressing the 'play' button. Pretty sweet, eh?” he says, and starts the video. The family then hear Hutz's voice dubbed over the late Mrs Bouvier's moving lips declaring "To my executor, Lionel Hutz, I leave $50,000!" When the family members protest, he sighs: “You'd be surprised how often that works, you really would.”

Professor Gary Slapper is Director of the Centre for Law at The Open University

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