Sam took his latest step up the international ladder in September 2010 when he made his debut for England U19s against Slovakia at Crewe Alexandra FC whilst still a year younger than most of his colleagues.
The Manchester United stopper had already been capped for his country at U16 and U17 level in the previous few years so has accumulated plenty of experience on the international stage.
Sam was also part of the England U17 group which became European Champions in May 2010, when he started the Finals in Liechtenstein as Head Coach John Peacock's first choice goalkeeper.
However, when he was given a rest in the third group game after the first two victories, he couldn't reclaim his place from Jack Butland in the latter stages. That is something which Peacock has since gone on record as saying was one of the toughest decisions he's ever had to make as Head Coach.
A tall and athletic goalkeeper, who is also adept with his kicking ability, Johnstone is highly regarded at Old Trafford too.