Sometimes Ralph Fiennes finds it hard to let go. He loved playing Charles Dickens so much in The Invisible Woman that he was reluctant to shave his beard off at the end. ‘I kept telling myself we might have to reshoot some scenes.

I lived with this beard for eight, nine months, and when I finally shaved it off, it was traumatic. I do feel a sadness at letting characters go. There is always a sense of saying goodbye.’

The irony is that Fiennes almost didn’t grow the beard, because he was initially reluctant to play Dickens. He jumped at the chance to direct Abi Morgan’s adaptation of Claire Tomalin’s acclaimed biography of the same name. But having directed himself in the title role of his coruscating contemporary take on Shakespeare’s Coriolanus, Fiennes was aware of just how exhausting it is to be on both sides of the camera. ‘Finally, after making approaches to another actor and getting nowhere, I could feel it coming. I knew I’d have to squeeze my brain again.’

The simplicity of the story – in which Dickens has an affair with a young actress called Nelly Ternan, played with great poise by Felicity Jones – was a stark contrast to the complicated life of the writer. ‘I’d always neutralised Dickens as an area of interest, so had only previously read Little Dorrit… As soon as I started work on The Invisible Woman, I discovered Dickens was extraordinary, complicated. I feel defensive when people say he was a shitty man. I defend the totality of Dickens.’

The Invisible Woman is, however, careful not to venerate Dickens. Instead it offers a fascinating portrait of the emotionally complex writer at the top of his game in the mid-1850s. Fiennes gives a contained, perfectly judged performance as the most lionised writer of his era. A particularly memorable scene shows Dickens being mobbed by the public at the races; a proper celebrity long before the word was sullied.

Fiennes himself has an odd relationship with fame: doggedly private, he wants to be known only for his work. He also shares Dickens’ tireless work ethic. Now 51, he is a veteran of Shakespeare and has regularly thrilled on the big screen, notably in Schindler’s List, The English Patient (he was Oscar-nominated for both) and The Constant Gardener. As Lord Voldemort in the Harry Potter films he was feared by many children.

There has, in the past, been talk of Fiennes being fierce in real life, too. He himself has admitted he has to sit on his anger, especially on set. ‘I once lost my temper in a situation and it just felt that all the reserves had gone. I was naked in my anger. I had exposed myself too much. I’ve always regretted the times I’ve let my anger out. I’ve realised there are ways of signalling something and staying in control.’

His honesty is as impressive as his ambition. After falling in love with Russia while acting in David Hare’s adaptation of Ivanov over there, he recently returned to film Ivan Turgenev’s 1872 play A Month in the Country. In Russian. ‘It was tough,’ he admits. ‘I was right out of my comfort zone. Language is important to me and there I was with severely limited Russian, learning a whole text.’ He grins. ‘Russian is a profoundly difficult language, so God knows if they’ll re-voice the whole bloody thing.’

As well as being super-bright and focused, Fiennes also has a great sense of humour. Look no further than the trailer for Wes Anderson’s upcoming The Grand Budapest Hotel, in which he stars as an hilariously camp concierge called Gustave H. In a cast that also includes Bill Murray, Adrien Brody, Tilda Swinton and Edward Norton, Fiennes shines. ‘Wes wrote a brilliant, funny script. His ear for comic timing is very, very good. I have some great one-liners.’

And best of all? Fiennes got to grow more facial hair – this time a manicured moustache. ‘I groomed it every day,’ he says, absently stroking his upper lip. ‘It mattered to me that it looked absolutely perfect for the part.’