The mutual attraction that blossomed on the set of Planet Of The Apes - despite her prosthetic mouth, lowered brow, ape's hair and false teeth - led to them setting up home, in a most unusual fashion, in Hampstead.
The house used to be two separate dwellings. Now, one belongs to Tim and one to Helena.
Each has its own very distinct decor: hers is girly, vintage and chintzy, while his is a gothic melange of 'skeletons and weird things' and floor lights in neon shades. Each partner has their own television, their own Sky Plus and their own kitchen - although Tim's is barely used.
At night they sleep in their respective dwellings. Not only is Tim an insomniac who likes to pace and watch TV, he says that she talks too much and that he needs some peace and quiet away from her. And anyway, counters Helena, he snores.
And yet there is the occasional blurring of boundaries since Helena has a craft room in Tim's half of the house where she likes to print hearts onto fabric and stitch ribbons onto mob caps.
She has, as followers of her distinctly 'shabby-chic' style will testify, a weakness for fripperies such as broderie anglaise and bobbles.
The two studio houses are joined by a ground level communal room, which is essentially a very grand hallway. Recently, a third home was purchased in the street which is home to the nanny and the couple's two children, Billy Ray, six, and Nell, two.
So how on earth does it work?
'He always visits, which is really touching. He's always coming over,' says Helena of Tim, in a way that suggests she considers this a perfectly normal version of cohabitation.
It's a rather rum state of affairs, but Helena enthuses: 'It really is a great idea. You never have to compromise emotionally or feel invaded.'