When Fran Unsworth becomes director of the World Service on 8 December, she will take control of an institution at its most important crux since the BBC and the government took the great leap of faith required to continue overseas broadcasting in 1946, after the immediate exigencies of the war had melted away and in harsh austerity conditions.

The World Service finds itself at such a moment because at the BBC’s last charter renewal, negotiated over just nine days in 2010, the then director-general, Mark Thompson, agreed the BBC should take over its funding from the Foreign and Commonwealth Office. That change – largely unremarked and undebated – came into effect in April this year. The World Service is no longer paid for by the government but by British licence-fee payers.

This change may look like a mere glide of the bureaucratic pen. It is not. It has several important consequences. First, the World Service must now compete for (ever-tighter) funds within the BBC, making its claims against those of drama, comedy, local radio and the rest. Second, the director of the World Service has less clout internally than hitherto; Ms Unsworth’s predecessors had the standing associated with those who had direct dealings with the foreign secretary, and most sat on the executive board of the BBC. The World Service these days looks more and more like a department of BBC News rather than a distinct entity with its own culture and ethos. Third, the World Service has to justify itself to licence-fee payers. The penny-watching citizen, faced with a bill of £145.50, might well ask why she or he should pay (by way of example) for a Hausa-language service in Nigeria.

In short, unless a case for its particular purpose is made before the next charter renewal (which must occur before 1 January 2017), there is a risk that the World Service will disappear into the great soup of BBC international newsgathering. You could argue that if this were to happen, it would not matter. That the romantic Bush House days of eastern European exiles, wreathed in cigarette smoke and earnestly debating Soviet politics, are long gone. That the era in which a shortwave World Service transmission was the listener’s only possible access to accurate reporting is over. That the World Service is an outmoded remnant of Britain’s imperial past. This would be an astonishingly shortsighted view. For many of its 191.4 million-strong audience, the World Service simply is the BBC – carrying the best of Britain to the world beyond its shores, and revered to an extent unimaginable inside the UK, where government suspicion of the BBC is amplified by noisy hostility from the rightwing press.

The World Service has a reputation and brand that other nations would kill for as they strive to increase their soft power by any means possible. For £245m per year, that looks a bargain when countries such as China are pouring billions into overseas broadcasting, while only last week the Kremlin-backed Russia Today began its UK television channel, available to British households via Freeview. Perhaps more subtly, but no less crucially, is the effect of the World Service’s relationship with its overseas audiences on the BBC as a whole.

Take that Hausa service as an example. The BBC has one foreign correspondent in West Africa. Its Hausa service has 28 staff. They bring a special depth and understanding to the BBC’s coverage of the region – from which all licencefee payers benefit. It was World Service Hausa journalists who broke the story of the abduction of Nigerian schoolgirls by Boko Haram. Far from being an tired vestige of empire, this multinational workforce mirrors the multicultural, polyglot Britain of the 21st century.

Historically, the BBC has been hugely imaginative and ambitious in its understanding of the possibilities of overseas broadcasting. Now is the time for it to show that same mettle again. It must put the World Service at the heart of its charter-renewal negotiations, and to forcefully argue its case as a public good. The government in turn needs to rise above political arguments about the fairness or otherwise of the licence fee and recognise the value of the World Service to Britain’s national interest.

There are endless possibilities for a refreshed and strengthened BBC World Service in the digital age. Innovations such as its Ebola information service for West Africa on WhatsApp may help point the way. Now, more than ever, the world needs a signal amid the noise; truth amid the dross. We must not let the World Service slip carelessly through our fingers.