Clarke said that Skanska was disappointed with his decision to leave but had been understanding. He said: "It wasn't particularly happy, but it was supportive – I'm only working three months of what is a formal 12 months' notice period. I had probably outlived my usefulness there to a degree."
He dismissed talk that he would struggle to establish a strong relationship with chairman Mike Jeffries. Clarke said: "I'm very comfortable with Mike. I like people who are a bit pushy. I find it easier; it's more fun."
Clarke was speaking after Atkins' annual results last week.
After a disastrous 12 months caused by an IT systems failures, the company posted a pre-tax loss of £61.6m – last year it had a pre-tax profit of £20.9m.
But Jeffries said that the business was essentially strong. He said: "The board is confident that the benefits from the group's cost reduction programme and stronger focus on operations will lead to a significant recovery in performance."