The London Irish back had feared that his England chances were blown after discipline problems last season.
The 27-year-old received an eight-week ban after an altercation with an anti-doping official, and also picked up a three-week ban towards the end of the season after striking Northampton’s Stephen Myler.
However, Armitage was still called up to Johnson’s preliminary training camp of 45 players, and now hopes to make the cut when the squad is trimmed to 30.
“There were times last season when I sat there and thought that I had messed up everything,” Armitage told The Telegraph.
“But now I've been given a second chance and I'm grateful for that. It has given me a new focus and I don't want to give the coaching team any reason to leave me behind. If it means me staying out for an extra 20 minutes at training, that's exactly what I will do.”