It is a truth universally acknowledged that any party seeking power in this country must first pay obeisance to Rupert Murdoch. Gifts must be laid at his feet, however humiliating that may be to the party in question. Now here comes David Cameron's prize offering.

A new Tory policy launched this week promises to allow Murdoch to bring his Fox News style to Britain. Old impartiality rules for news broadcasting will be scrapped for all except the BBC. That means abandoning the culture of broadcasting balance that Murdoch has always felt stifling for Sky News. No-holds-barred shock-jock television news and current affairs would replace the seriousness of Adam Boulton. For those who have never sampled the joys of Murdoch's Fox News, it is an eye-popping spectacle to British viewers. Raucous, brash, aggressive and ultra-rightwing, it would arrive here with the same cultural impact that the Sun had on British newspapers. There are few serious media observers, apart from those in Murdoch's pay, who do not see his arrival in Fleet Street as marking a steep downward path for the British press.

The attack press we have now that so shocks European visitors is mainly thanks to the man who controls more than 40% of newspaper readership. Allowed to run Sky untrammelled, his dominance of both press and broadcasting would be unthinkable in almost any developed nation: the United States has far stricter cross-media ownership rules. Possibly only Italy could compare with Britain for lax media ownership regulation, where Berlusconi is about to prove yet again this week that he who controls most of TV and newspapers can control elections. Murdoch never harboured personal political ambition - only to sway countries to the right and keep them there. The opportunity to pump out Sun-type broadcasting will warm his enthusiasm for David Cameron, who is otherwise not quite right enough to have earned total Murdoch approval.

The Tory document attacks the BBC as being liberal-biased. With great glee, its opening paragraph quotes Andrew Marr apparently agreeing. But Marr had spoken once of an "innate liberal bias" in the context of a long and thoughtful discourse on the BBC's perpetually self-critical striving for fairness and balance, unique in all the media. Responding to the Tory policy, he warned politicians yesterday: "If you want partisan and biased broadcasting, just you wait. You have no idea how demeaning it will feel for you. Broadcasters will become like bloggers, but with vastly more firepower, as they rip into you just as newspapers do. Be careful what you wish for." Some say the BBC would stand to gain, as the only non-partisan voice, but wiser heads warn that the BBC would inevitably be sucked towards the new rowdy Fox News culture.

The Tories' other main recommenation will also delight Murdoch. It is to top-slice the BBC licence fee and spread the proceeds to other broadcasters. Murdoch has always used his newspapers to undermine the BBC, claiming it damages the free market in broadcasting - as indeed it does, and as indeed it should. The media is not like other markets: lack of competition has often been the guarantee of media quality. Radio 4, Radio 3, BBC4, CBBC and CBeebies, programmes like Newsnight and the Today programme, flourish in competition-free zones.

American newspapers often follow the same pattern where one-newspaper cities sustain the quality of a Washington Post or a San Francisco Chronicle. In the UK, since the Beaverbrook-Northcliffe battles, too many newspapers have fought each other downhill, shouting ever louder to be heard on overcrowded newstands. The BBC needs competition, say the Tories, but that is dogma, not an honest evaluation of what competition has historically done to BBC quality. People complain most about BBC output when it has to compete hardest. What else but trawling for viewers makes BBC News sometimes lead on Heather Mills or gruesome murders? No, the BBC is never perfect, and we rightly subject it tougher quality expectations.

At first glance, taking money from the licence fee to give to others who produce good but unprofitable programmes looks innocuous. Isn't this just special pleading by the BBC to want it all? But spreading the money around breaks the direct link between viewers and the BBC: there is strong support for paying the licence fee, with a majority willing to pay more than the present £2.60 a week. Its transparency is popular: licence-payers see where the money goes and who to blame if they don't like it, not pepper-potted around among commercials on other channels. Some quango handing out money to specific "programmes of merit" would attract the same opprobrium as the lottery funds. The BBC already contracts out 30% of output: a new bureaucracy handing out small sums would syphon off more in administration. And all for what? Channel 4 needs a new funding system now ITV can no longer bear the cost. So why not make all profitable broadcasters pay a small levy to pay for C4's public service remit? Why shouldn't Sky pay?

When considering value for money, Sky's revenue is £4.5bn, compared with the BBC's £2.5bn for TV and online. But how many memorable programmes has Sky ever made? In terms of viewing, in a week the BBC gets 42% of viewers, ITV 22.7% and Sky 6.8%.

There will be a tough fight to defend the BBC. Michael Grade, the former BBC chairman and now head of ITV, waded in yesterday: "Were I still chairman of the BBC I would be arguing that to distribute monies given by the British public exclusively for BBC use to other bidders feels like a breach of contract. The public should be asked if they are happy to have their BBC dues used for any other purpose."

Saving the BBC from Murdoch-pleasing predators should be clear blue water between the main parties at the next election. Alas, not so. James Purnell, the previous culture secretary, announced that top-slicing the licence fee was on the cards. Perhaps the new culture secretary, Andy Burnham, would kick it into the tall weeds where it belongs? If Britishness means anything, it means the BBC. No, depressingly in his first statement, he hastened to agree it was indeed an option. Yet again, Labour legitimises a Tory policy. Only the Lib Dems denounce cutting licence fee funds as "a disaster for the future of the BBC and public service broadcasting". If there is to be a hung parliament, here is another reason why the Lib Dems might improve either party in power.

polly.toynbee@theguardian.com

· This article was amended on Tuesday April 1 2008. An editing error left the article above suggesting that the BBC's revenue is £2.5bn. That sum represents only the revenue from the BBC's television and online activities. This has been corrected.