Kenneth Branagh: Luvvie in a cold climate

Branagh is no stranger to ambition: he dared to take on Olivier at the age of 26, and wrote his autobiography at just 28. But in recreating Sir Ernest Shackleton's heroic Antarctic journey of 1914, was he facing up – at 41 – to a challenge too far?

This parting was well made..." The actor Kenneth Branagh, who has arguably done more than any man alive to popularise the works of William Shakespeare, and whose fondness for wordplay shines through The Play What I Wrote, the homage to Morecambe and Wise what he in fact directed, will perhaps forgive me for applying a line from Julius Caesar (Act V scene 1) to his spellbinding portrayals of two very different men with two very different haircuts.

In Shackleton, to be shown this week on Channel 4, Branagh plays the British polar explorer Sir Ernest Shackleton. He has dark hair with a neat fin-de-siècle centre-parting, whereas as SS General Reinhard Heydrich in the forthcoming BBC2 film Conspiracy – a performance for which he has already won an Emmy and is in the running for a Golden Globe – his hair is Aryan blond with a razor- sharp side-parting.

By contrast, the man I meet at the Channel 4 offices in Horseferry Road, London, has no discernible parting, nor, at 41, any discernible grey hairs. He is courteous and charming, although his charm is laced with the wariness of one whose private life so excites the press.

He is perhaps right to be wary. In the United States, say, or France, he would be feted as a national treasure. Here, there has always been at least as much sniping as praise. "Hell, not even OJ Simpson gets a press as bad as that," said an American studio executive on reading some of the digs at Branagh.

The cuttings are full of them. "The greatest act of hubris since Prometheus absconded with the rights to divine fire," snorted a reviewer when Branagh dared to beg comparison with Laurence Olivier by remaking Henry V when he was only 26. Hubris has always been a favourite word among Branagh-phobes. When he then wrote his autobiography at 28, apparently to help finance his theatre company Renaissance, he was, suggested someone at The Guardian, doubtless a classics graduate, "overdosing on hubris. Is that nemesis waiting in the wings?"

The knocking got louder during his marriage to Emma Thompson, and unpleasantly triumphant when the marriage failed. Yet the object of all this bile – not to mention a fair amount of adulation, of course – seems surprisingly mild-mannered, evidently no less cowed than I am by his forbidding, if admirably protective publicist, who sits in on our encounter and keeps leaning forward to insist that we talk only about Shackleton.

We are not permitted to discuss Heydrich, Eric and Ernie – a trio of names that rather sums up Branagh's impressive versatility – so heaven knows how she might react if I were to utter the names Emma or Helena (his former squeeze Helena Bonham Carter). Still, when she slips out for a few minutes, we fall hungrily upon his other projects. In the meantime, in fairness, Shackleton is an immensely rich topic on its own.

The two-part drama chronicles the most heroic of failures, the explorer's 1914 expedition to cross Antarctica. When his ship Endurance was crushed by ice before actually reaching the continent, Shackleton led his men in three rowing-boats through the melting ice to the uninhabited Elephant Island, from where he and a small crew set out on the appallingly perilous 800-mile voyage across the Weddell Sea to South Georgia; their aim to get help from a whaling station there.

But even having landed on South Georgia, they still had to cross a mountain range to reach the whaling station. Shackleton finally returned to Elephant Island four months after setting off. His men were all rescued, with the loss of some frostbitten toes but no lives. With tragic irony, however, some of them later died on the Western Front, having survived the worst that nature could throw at them.

The towering achievement of this BBC production – made by the team behind the award-winning Longitude, writer-director Charles Sturridge and producer Selwyn Roberts – is in making those unimaginable conditions imaginable. Filming took place over five weeks in Greenland, on ice floes that were scarcely less treacherous than the ones Shackleton confronted; indeed the hostile environment helped the cast nail their characters.

"There was intense emotional bonding, great generosity and a fantastic amount of banter, with everyone being ribbed senseless all the time and some filthy nicknames," Branagh recalls.

"But there was also a near-riot one afternoon. The conditions make you peculiarly hungry and potentially cranky, and when people realised that someone who'd just arrived had brought a bag of Mars bars, it was like watching a group of rats. The woman with the bag was almost savaged, and afterwards people were getting quite narked that person X hadn't shared their Mars bar. Shackleton's diaries, and the diaries of others on the expedition, contain an obsession with that kind of detail."

Branagh was himself obsessive in researching Shackleton's life, scrutinising books and diaries and archives. "Despite being knighted he was something of an outsider, clearly a flawed human being. He was a man's man, prolific in his relationships with women, who famously had a relatively public mistress. There was a revealing moment on a trip he made with Scott in 1901, following a moment of indiscipline with a drunken crew member. Scott was completely flummoxed, so Shackleton said 'May I have a word?' and before the man could remonstrate, slugged him, knocked him down.

"It's part of what made him a complicated geezer. He didn't mind rolling his sleeves up, and was a classic example of not asking you to do anything he wouldn't do himself.

"Nor was he crushed by not reaching the South Pole first. Being first was less important than being engaged in adventure, that old-fashioned English thing of it not mattering whether you win or lose, it's how you play the game. There's a famous quote: 'For scientific discovery give me Scott, for speed and efficiency of travel give me Amundsen, but when your back's against the wall and no hope is left, get down on your knees and pray for Shackleton.'"

I ask Branagh whether he thinks he resembles Shackleton in any meaningful way? He pauses, considers. "I suppose I have put myself in positions of risk and vulnerability, though not remotely as bravely as Shackleton. I have attempted to take the path my gut tells me, not what I was supposed to do."

Hence, perhaps, the part of Heydrich, who got under his skin more than even Shackleton did. If playing the explorer was the most uncomfortable experience of his acting career physically, then playing Heydrich was by far the most uncomfortable psychologically.

Conspiracy, a collaboration between the BBC and Home Box Office, brings to horrifying life the Wannsee Conference of January 1942, at which top Nazis worked out – in less than two hours – how best to rid Europe of its Jews. Branagh's performance as Heydrich, who chairs the meeting, is horribly riveting, somehow embracing charm, wit, and pure menace. His stern publicist having briefly vacated the room, I ask what on earth appealed to him about the part.

"I have a fantastically privileged job," Branagh says, choosing his words carefully, "and if it forms some larger purpose than entertainment – which it seems to me is a significant goal in itself – then in Conspiracy it is the illumination of certain parts of the Holocaust experience, and in Shackleton the story of how important it is to preserve life, value life and enjoy life while we have it.

"Heydrich seemed to me a man so unremittingly without morals, but we heard a rumour that his brother had read a letter from him, then tore it up, and from that point on devoted himself to Jewish affairs, to some restitution of the family's reputation. Naturally, historians are desperate to know what was in the letter, whether it was a confessional document or perhaps an outline of quite what he had been up to. I find little snippets like that fascinating. They feed into the ongoing search to find whatever it is that explains human motivation in a way one can convincingly put into performance."

With Shackleton, Heydrich, and Henry V already on his CV, it seems reasonable to ask whether any other historical characters tickle his fancy. "Samuel Pepys is one who intrigues me," he says. "And I have just been narrating a piece about Chaplin's film The Great Dictator. It is impossible not to be grimly and awfully fascinated by Hitler. The possibility has come up a few times."

Which brings us, or rather doesn't bring us, to Eric and Ernie.

Branagh's boyhood in working-class Belfast, then in Reading from the time he was nine, must often seem like something that happened in another lifetime. But he revisited it when directing The Play What I Wrote, which is currently playing to delighted audiences at London's Wyndham's Theatre.

"There is something about the current time that responds very well to two hours of comedy without irony," he says. "We've had a lot of Americans in, thank God, who don't know the first thing about Morecambe and Wise but seem to respond to people throwing imaginary things into paper bags.

"Of course, we all have our memories of Morecambe and Wise. I remember their show going out on a Friday night. My mother would be out at bingo, my brother was usually out as well, and so I'd sit there laughing with my dad. I remember it being very good to be laughing with my dad at the same thing. It was innuendo without smut, with a genuinely anarchic content. Some of it was truly surreal, like that Arthur who'd come on and play the harmonica.

"I even wrote to them once wanting tickets for the show. And I remember a documentary about them that I was completely riveted by. Places such as the BBC rehearsal rooms in Acton seemed to be the most glamorous places I could imagine. And that address where I sent my letter – W12 8QT – it was like some sort of magical number."

Speaking of magic, we haven't yet touched on Branagh's next role – Gilderoy Lockhart in the second Harry Potter film, Harry Potter and the Chamber of Secrets. But I wouldn't want to push my luck.

'Shackleton' is on Channel 4 at 9pm on 2 and 3 January. 'Conspiracy' is coming soon on BBC2

Deborah Ross is away