3i, the UK-listed private equity group, has agreed to invest €225m ($357m) for a 17 per cent stake in Unión Radio, the Spanish radio operator controlled by Prisa, the Madrid-based media group.

The investment is a precursor to a planned flotation of Unión Radio in the US or Spain, said 3i. It plans to bulk up the company through acquisitions in its key growth markets of Latin America and the Hispanic-speaking parts of the US.