The Guardian. "I had two famous guys in mind to play the aging rocker Billy Mack, and I couldn't decide who to ask. But at the read-through, Bill did it so perfectly he became a definite yes.
The website celebsbar.com is an aggregator of news from open sources. The source is indicated at the beginning and at the end of the announcement. You can send a complaint on the news if you find it unreliable.