RUPERT Murdoch's chances of taking over Britain's Channel 5 TV were considerably reduced, but not entirely eliminated, when the Government agreed on Wednesday to include a “plurality test” in the Communications Bill now moving through the House of Lords. If this concession had not been made the Lords would probably have blocked the Bill which contains several other useful measures. The new test will require the Communications Regulator to assess the likely effect on diversity of opinion of any purchase or merger among major UK media owners. Under existing regulations Mr Murdoch's ownership of several British newspapers disqualifies him from owning a terrestrial TV station but the Government - for reasons that are only too obvious - wanted this restriction removed. Lord Puttnam, the film producer who negotiated this compromise, deserves credit for his initiative and persistence. Unfortunately, however, he has dropped his opposition to another provision of the Bill which will enable American TV or film interests to buy or invest in the UK's ITV channels. There is no case for this change. The government has talked about encouraging free trade, but television is not just any old commodity - it is a force of profound cultural influence. And, in any case, since foreign companies cannot own American TV or radio stations why should the UK open its doors to US producers whose product is already more than adequately represented on its screens? The Communications Bill will tidy-up and improve the relationship between government and broadcasting media. However, the inclusion of the so-called “Murdoch” clause and the provision for foreign purchase were totally unnecessary and have cast doubt on the Government's motives.