The Doctor will resume hostilities with the Daleks when the former Time Lord David Tennant returns for the 50th birthday edition of Doctor Who on Saturday.

But the much anticipated anniversary show, The Day of the Doctor – which will be simulcast in nearly 100 countries and shown in nearly 1,500 cinemas in 3D – will also resonate in a battle that is taking shape rather closer to home, over the future of the BBC.

The BBC's controller of drama commissioning, Ben Stephenson, said Saturday's episode, the culmination of a week of programmes around the Saturday teatime series, was a celebration not just of Doctor Who but of the BBC itself.

The corporation has long been targeted by the Tory party whose chairman, Grant Shapps, warned last month that it could lose some of the licence fee, the first shots in a debate about the future of the BBC ahead of the renewal of its royal charter in 2016.

But it has also come under fire from one of its most respected presenters, Question Time host David Dimbleby, who this week suggested it was "too powerful for its own good", echoing concerns of its former executive and Olympics supremo Roger Mosey, who earlier this month questioned the need for BBC3 and BBC4.

Stephenson, who oversees the BBC's entire drama output, said: "There are quite rightly a lot of people with strong opinions about the BBC.

"The very best way to defend ourselves is to stand up for the core of what the BBC is about, making the highest quality of programmes for all audiences for which people feel it is worth paying the licence fee.

"We have got to be better at standing up for ourselves. There is no other drama in the world that is like Doctor Who, with its history and level of ambition. I don't think it's any coincidence that it came out of the BBC.

"It is absolutely in a nutshell what the BBC stands for in terms of real creativity, allowing the audience to go on a special type of journey unimpeded by commercial considerations.

"Sometimes it fails but when it works, it works spectacularly and can be exploited globally.

"The future of the BBC will be fought on the quality of the programmes. It is a rallying cry I really believe in. We offer the broadest range of content of any producer in the world. "

Huge secrecy surrounds Doctor Who's 50th birthday show, which will see the return of Tennant and his companion Billie Piper, alongside the outgoing incumbent Matt Smith and special guest star John Hurt.

Already the BBC's biggest drama export, the special 75-minute edition will be one of the corporation's biggest ever simulcasts. Due to be shown simultaneously in 94 countries around the world, it is the sort of global broadcast usually reserved for international football tournaments and royal weddings.

It will also be shown in 3D in 1,450 cinemas, around 400 of them in the UK. In the US, where it will be shown on BBC America, 10,000 cinema tickets were sold out in 28 minutes.

Exported to more than 200 countries, Doctor Who is one of the BBC's five biggest earners, alongside brands such as Top Gear and the international version of Strictly Come Dancing, which last year together generated revenues of over £300m.

Adam Waddell, director of entertainment brands at the BBC's commercial arm, BBC Worldwide, said: "It's one of the BBC's oldest programmes and also one of the most loved. It is really important for the BBC and its reputation globally.

"In America, the home of the big blockbuster drama, we are now competing on a level footing and have seen a real surge among teenage viewers."

Although Doctor Who is only watched by about two million viewers on the BBC America cable channel, it has been watched almost 200 million times in the US on online TV service Netflix, and was the top selling series on iTunes.

BBC Worldwide said the cinema screenings, for which fans will have to pay, was not "overtly commercial" but an extension of the celebrations around the anniversary show.

"We are not looking to make an awful lot of money from cinema," said a spokesman. "We are more interested in helping more people see the episode in 3D."

Stephenson said the appeal of the show lay in its "ingenious format which means you can go anywhere, anytime … and he can regenerate into other doctors.

"As well as the villains – the Cybermen and the Daleks – at the heart of it is the doctor," he said.

"He is curious about the world, excited by it, and he is always looking for another adventure. It's a show about the love of life."