3i, Europe's largest venture capital group, has made a return of more than 400 times its money on an investment that has been sitting in its portfolio for more than 30 years.

The sale, which made 3i £20.5m (€29.5m) on its initial £40,000 investment, is a long way from the private equity industry's average of three-to-five years' incubation until disposal. It bought the stake in Jackson Building Centres, a UK building merchant, 34 years ago.