Where a policyholder has deliberately damaged his own property, any insurance he has taken out over that property will not cover such damage, unless the policyholder can prove that he was legally insane at the time. The test of insanity is the same as is used in the criminal law.

The important High Court judgment of Mr Justice Coulson in Porter v Zurich [2009] EWHC 376 (QB) has, for the first time, indicated that this proposition is true in English law. Any lesser degree of psychiatric disturbance, including even quite severe mental illness, will not absolve a policyholder of having to take responsibility for damage he has deliberately caused.

The claimant, Mr Porter, had suffered a number of disastrous events in his life, developed a psychiatric disorder and displayed symptoms of delusions and depression.

Mr Porter attempted to commit suicide by setting fire to his house and staying inside while it burned down. He changed his mind before he was overcome by the fire, and escaped, but his house was rendered uninhabitable.

The judge found that Mr Porter would be unable to recover under his home insurance policy unless he could prove that he had been insane when he set the fire. The test of insanity was that contained in a famous criminal law case, M'Naghten's Case, namely that:

"it must be clearly proved that, at the time of the committing of the act, the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the quality of the act he was doing; or, if he did know it, that he did not know he was doing what was wrong."

On the psychiatric evidence before him, the judge found that Mr Porter set the fire "in a clear and deliberate way," and in the knowledge that what he was doing was wrong. Even though Mr Porter was suffering from a delusional disorder at the time of the fire, he had not proved that he was insane, and so he could not recover for the fire damage under his home insurance policy.