Speaking as someone who left CH2 & joined Atkins 5 yrs ago, I was somewhat amused by the article. Am I going to end up going full circle?!
While I don't have the ear of Atkins' Chief Exec, I would be surprised if this went any further though. It would dilute the margin of Atkins which is much more profitable as a % of revenue, and (as a plc) I think has a stronger cash position.
That's not to say that there could be continuing strategic collaboration though, such as the current Crossrail2.