Trade and industry secretary Alistair Darling said he has asked media regulator Ofcom to conduct an initial investigation Sky's acquisition of a 17.9% stake in ITV.

The request says Ofcom must provide advice to the minister by April 27 on whether the case raises public interest concerns about the number of different owners of media enterprises.

The Office of Fair Trading announced on January 12 it would examine BSkyB's stake to establish whether it constitutes a "relevant merger situation" under the provisions of the 2002 Enterprise Act.

Sky acquired a 17.9% stake in ITV in November, scuppering any plans for a takeover of ITV by Virgin Media, formerly NTL, which was being muted by the company at the time.

Under "cross-ownership rules", Sky is not allowed to own more than 20% of ITV.