Prenuptial agreements are binding when ‘fair’ and entered into freely, the Supreme Court ruled today. The ruling has left Nicolas Granatino, the divorced husband of German heiress Katrin Radmacher, with just £1m of his ex-wife’s estimated £100m fortune.

When the couple married in 1998, they signed a prenuptial agreement that neither party was to acquire any benefit from the property of the other during the marriage or on its termination. The couple separated in 2006 and Granatino applied to the High Court for financial relief. He was granted £5.85m. Radmacher appealed this, and the court of appeal, giving greater weight to the prenuptial agreement than the High Court, reduced the sum to £1m.

Granatino appealed the decision to the Supreme Court. It dismissed the appeal by a majority of 8-1, ruling that a court should give effect to a prenuptial agreement that is freely entered into by each party with a full appreciation of its implications unless, in the circumstances prevailing, it would not be fair to hold the parties to their agreement.

Simon Bruce, Radmacher’s solicitor and head of family law at London firm Farrer & Co, said: ‘This decision means prenups are binding as long as they are fair. Prenups are like a form of fire insurance – better taken out before the event rather than after it. Couples can now decide in the best of times what the outcome would be in the worst of times.’

A spokeswoman for London firm Payne Hicks Beach, which represented Granatino, declined to comment on the judgment.