BSkyB faces a potential loss of £343 million as a result of being required to cut its shareholding in commercial television company ITV plc to below 7.5%. It may not have turned out to be such a good long-term investment. Since effectively blocking rival cable company Virgin Media from acquiring the terrestrial television network, the value of its stake in ITV plc has almost halved.

BSkyB paid above market price at 135 pence per share to acquire just below 18% of ITV plc for £940 million, prompting rival operator Virgin Media to abandon its bid for the broadcaster.

With ITV shares now trading at nearer 75 pence, the pay-television company faces a considerable loss in reducing its stake but may have achieved a strategic gain in distracting its competitors.

The Competition Commission stated that BSkyB must reduce its stake to below 7.5%, a view upheld by John Hutton, the secretary of state for business and enterprise and regulatory reform. Sky said that the company will give “careful consideration to the announcement and confirm any further steps in due course”.

Sky has four weeks to decide whether to appeal for a review of the decision. It also successfully argued that it should not have to disclose the period in which the divestment of shares is to be completed. As a result, the process could be protracted, leaving ITV weakened and Virgin Media out of the game.

James Murdoch, the chairman of BSkyB, has described the stake in ITV a “long-term investment”. It may well yet turn out to have been a shrewd strategic move.

BSkyB still faces a review into pay-television by the communications regulator Ofcom, launched after complaints by Virgin Media and others.

Despite the drop in value of its investment in ITV, BSkyB is expected to report strong operational performance. ITV shares are meanwhile at their lowest level in four years and the value of Virgin Media has also plunged.