By Luke Baker

LONDON (Reuters) - The Court of Appeal has ruled that a pre-nuptial agreement made overseas is still valid in Britain, a decision that could have far-reaching implications for those going through divorce.

In a high-profile case involving a German heiress who was married to a French investment banker, the three-judge panel ruled on Thursday that the agreement, signed in Germany before the couple married in London, was valid under English law.

"The Court of Appeal, in a carefully reasoned, thoroughly modern judgment, has enabled English matrimonial law to catch up with the rest of the world," Ayesha Vardag, a solicitor for Katrin Radmacher, the German heiress, said after the ruling.

"From today, grown-ups can agree in the best of times what will happen in the worst of times."

Radmacher, 40, married Nicolas Granatino in 1998, a few months after signing a pre-nuptial arrangement in which they agreed that he would get nothing if they divorced.

Their marriage began to break down in 2003, after Granatino, 38, gave up his high-paying job working in emerging markets for JP Morgan to become a biotechnology researcher at Oxford University earning 30,000 pounds.

"When we met and married, Nicolas and I were broadly on an equal footing financially," Radmacher said in a statement released after the ruling.

"He too is an heir to a multi-million pound fortune and when we met was an investment banker earning up to 330,000 pounds a year. The (pre-nuptial) agreement was at my father's insistence as he wanted to protect my inheritance.