Anderson was selected a year ago by Scotland coach Steve Clarke for matches against Cyprus and England. At the time, it was reported the midfielder had been forced out of the squad due to injury.
But speaking from England's training camp at St George’s Park, Anderson admitted, "I went away with the Scotland team and I left camp after a few days and decided I just needed more time to make my decision really.
"I didn't want to dive into anything so I'm really thankful I've done that now."
Anderson added, "‘I'm definitely English.
"That's where I see myself. It's just I hadn't really been called up to England throughout the ages when I was younger so I thought I'd take the opportunity to play. Once I got that belief that I thought I was good enough to play for England it hit me, and I focused on England."