In 1906, Arthur transferred from Peterborough AC to join the successful Birmingham club, Birchfield Harriers whose emblem is a stag with the motto "Fleet and Free." (It is for this reason Birchfield Harriers are frequently referred to as the Stags.)
The following year he won the Midland Counties Ten Miles title. The same season this versatile and seemingly indefatigable runner was runner-up in the two miles steeplechase, fourth in both the one and ten miles races and fifth over the four miles distance at the AAA Championships!
Although he was only with the Perry Barr club for three years, he achieved considerable successes in that time carrying all before him in the Olympic season of 1908. When he was crowned English National Cross Country Champion at Newbury that spring, the magazine Sport and Play reported the conclusion as:
"A stampede of people from the stand to the rails gave warning of the leaders' approach. It was seen that Robertson was out in front with a commanding lead and we all knew that his speed would get him home winner of the National Championship. Undistressed he came home, with his hands down - no side, no gallery play - a modest champion of the first order. Proud of his win, proud of his club."
Robertson went on to win the International Championship in Paris when a dominant England team impressively packed their scoring six runners into the first seven finishers.
He was runner-up in the 1908 AAA four miles championship, won two medals at the 1908 Olympics at London's White City Stadium, Gold in the three-miles team race, which Britain won ahead of the US and France, and silver in the 3,200m steeplechase.
This silver medal remains the only occasion that a Scottish athlete has won a medal in a steeplechase event at any international championship to date. He also placed fifth in the five miles race.
His brother DC was a member of the GB cycling team at the same Olympics.