The BBC World Service should be hived off. That is a recommendation likely to be read askance by those who were persuaded by John Tusa's typically robust defence on these pages recently of a broadcasting service he passionately loves, and which, he claims, has 140 million listeners around the globe. Yet it is a suggestion, we believe, that would save the essential and precious qualities of the World Service, while simultaneously giving John Birt, the BBC's director general, all that he would wish in his struggle to streamline the corporation and its finances.

We are not talking about auctioning shares in BBC World Service plc (although that might allow the service's many admirers to put their money where their mouths are). Instead, the proposition is that the BBC World Service be established as an independent corporation, free to contract with the BBC and anyone else to supply it with world news. A BBC World Service Act could make crystal-clear its freedom from political interference - unlike the mainstream BBC.

The ambiguous relationship that persists between the BBC governors, its politically appointed chairman and the government of the day remains one of the most worrying aspects of this occasionally maddening and perennially fascinating British institution. The World Service would be healthier outside. There is no reason to prevent it continuing to use the BBC tag. It would be easy to organise a transfer of the assets of the service to a board of governors. John Tusa might even be its chairman, provided he brings in some top-flight personnel and finance managers.

The BBC World Service actually has no organic links with the BBC's production centres in television or radio - which is the gist of Mr Tusa's case. It is a different animal altogether from the BBC's Worldwide Television. It is not even statutorily a part of the BBC. It is a non-departmental public body. Its finances are separate: the vast bulk of its income comes from the Foreign Office grant. Its journalistic culture is palpably different, as anyone who has been to Bush House to taste that marvellous polyglot atmosphere can testify. Its highly prized independence rests on the faith of its listeners that they are being treated as adults capable of hearing truthful accounts. That quality does not need John Birt, Sir Christopher Bland or proximity to Broadcasting House; it does need a positive sense of the World Service's purpose and virtues which would, we believe, be better guaranteed by its standing outside.

The official line from Bush House is that quality of news coverage would suffer if the World Service could no longer call upon the (domestic) BBC's foreign staff. But what is to stop an independent BBC World Service contracting with the BBC to buy in reports and feeds as needed - would not that fit very well with the contract culture introduced by John Birt?

Indeed hiving off the World Service ought to make sense to the Birtians. The director general of the BBC attracts extraordinary criticism - all the more extraordinary in that his critics often fail to identify the specific failings in output for which he is allegedly responsible.

The BBC's annual report, quite rightly, blows the corporate trumpet over some recent programming successes, notably in popular television, though it is rather puzzling to see Mr Birt somehow claiming proprietary rights over Ms Jennifer Ehle's cleavage.

But Mr Birt does have one signal failing, and it is an intellectual one: he has never convincingly argued in public why his admirable project of instilling cost-consciousness and direction into the loose baggy monster that is the BBC requires the organisation's existing boundaries to be maintained. This is not to rehearse tired arguments about Radio One, though anyone who regularly listens to the immensely entertaining but immensely self-interested Chris Evans will ask themselves what scintilla of public interest there is in any of this, bar the traffic reports and time checks. Any clear-eyed look at the extent of the BBC would conclude that local radio, for example, as well as the World Service, would be better off outside the broadcasting empire.

Mr Birt works by formulae. Chief among them is the idea of separating production from commissioning, as a way of better displaying costs. Thus the World Service is set to become a purchaser of programmes the bulk of which are to be provided by News and Current Affairs. But the alternative is to give the World Service autonomy. It is already a "cost centre" - runs its own budgets. Let it decide, within the limits of its revenue- raising capacity, where and what programmes and reports it wants, and where it wants to buy them. If it wants to use the BBC's Moscow bureau, fine; if it wants to use a feed from the Americans or Deutsche Welle, why not?

Tusa romance and Birt logic come together. Free the World Service. That of course solves none of its pressing operational questions, the main one being whether it can secure revenue additional to its Foreign Office grant, allowing it to expand, to introduce its style and qualities to new audiences, to new parts of the world. There is no point in pussy-footing. The issue is whether the service can and should take advertising, without corrupting its peculiar and peculiarly special culture of news and commentary on the affairs of the world. Resolving that issue - and the ever-present question of the World Service's independence from the government of the day - are not going to be made harder by its separation from the BBC. They may actually be made easier.