A worm that turned

From playing the most hated man in Britain to taking on the role of a tapeworm: 'It's not that much of a jump,' admits Alex Ferns, forever more to be known as EastEnders wife-beater Trevor.

But this is no ordinary parasite, it's the tapeworm that 'told' its host Demetrios Tsafendas to kill the architect of apartheid, South African prime minister Hendrik Verwoerd.

The incredible true story of Tsafendas - kept relatively unknown to the outside world by the machinations of the then South African government - is explored in ID, the first play by actor Antony Sher, which has its opening night at the Almeida Theatre this week.

'Lintwurm acts as Tsafendas's subconscious in the play, but he is also a kind of master of ceremonies, flipping between narrating and being in the scenes,' says Ferns. 'We didn't know initially whether to make him wormish or human with wormish qualities, but I will be looking very odd,' he grins.

Ferns was not, as one might assume, picked for his ability to terrify - although that cold, blue-eyed stare is still enough to send shivers down your spine. Rather, it was his knowledge of South Africa: he lived there for 17 years from 1980 and witnessed many of the country's seismic upheavals.

'Tony knew I'd spent some time in South Africa and asked me along when he started his exploratory workshops two years ago, so I've been involved from pretty much the beginning,' explains Ferns.

Those first sessions were a chance to take the text that inspired Sher - Henk van Woerden's biography of Tsafendas, A Mouthful Of Glass - and look at the theme of identity.

Verwoerd's assassin was the illegitimate son of a Greek man living in Mozambique, the result of an affair with a coloured maid. He was despatched at an early age to live with his grandmother in Egypt, during which time his family moved to Transvaal and left him behind.

So began 20 years of being shunted from country to country, with time at sea, in prison and in hospitals.

When Tsafendas finally managed to slip back into South Africa, despite being banned, he was outraged by the apartheid laws that stopped him from marrying a coloured woman and, amazingly, applied to be reclassified from white to coloured.