ITV has released it's press pack for Identity (thanks for finding it, riddler!) which includes and interview with Keeley Hawes.
An excerpt from the interview in which Keeley compares her character in Ashes to Ashes and Identity:
"Keeley is pleased to have had the chance to portray two very different women in the police force. “Both Alex Drake, in Ashes to Ashes, and Martha Lawson are strong women - in the jobs they do they have to be - but that is where the similarities between them stop. That’s why I chose to take on the role of Martha as they are both in completely different worlds playing by different rules. Drake is constantly in a life threatening position, Martha’s situation is less dramatic. That’s the great thing about what I do, you get to inhabit such different worlds.
View the entire interview HERE