A source told People magazine; 'They have been separated for a while... they have not been together for a few months.'
The unnamed source added that the reason for the split was hectic work schedules and other commitments that caused Kate and Len to grow apart from each other.
The source added that despite the break-up they are trying to remain friends; '[They] spend time together in LA when Kate is there.
'There has been no drama... It's just not Kate's style.'
Rumours began circulating several months ago, as Len hasn't been seen wearing his wedding ring for some time.
But London-born Kate, 42, went further to confirm the rumours when she appeared without a major accessory on the red carpet at the British Fashion Awards on Monday evening.
The wedding ring-less mum has, in newly single style, been hitting the town with two consecutive nights out since the news broke.
An insider said; 'Kate is not dating and is only focused on her daughter and work.'
The pair met on the film set of Underworld in 2003 and in a whirlwind romance married only a year later in May 2004 at a ceremony in Bel-Air, California.
The English actress, daughter of Porridge actor Richard Beckinsale, is currently filming the fifth film in the Underworld franchise in Prague.
Kate has a 16-year-old daughter, Lily Mo Sheen, from a previous eight-year relationship between 1995-2003 with actor Michael Sheen.
At the time Kate spoke about her 'embarrassment' that Michael never proposed; 'If you keep a library book out for long enough, you feel it's yours.'