The Broadcasting Commission of Ireland (BCI) has put a temporary freeze on any investor in commercial radio stations holding more than 17.9 per cent.

The move affects UTV, which holds that level of ownership, with businessman Mr Denis O'Brien not far behind with around 14 per cent.

The BCI said it would review its policy on ownership and control of commercial radio stations. The review, including public consultation, will begin in March. The new policy will become effective late next year.

The BCI said a degree of concentration had taken place in the sector in the last three years; the review would probably include an investigation of policy, and of whether the aims of diversity, plurality and diversity were being met.