Fortunately the strap broke before something more serious could have happened. However, no station staff came to his help when he was trying to get assistance to retrieve the contents of his bag from the tracks. Also as Londonist point out the comments by some Evening Standard readers, seem to place the blame on Roberts - saying he bought things on himself.
DeanN from Londonist wrote "While compassion isn't London's strong suit, blaming the victim is a little extreme, and clouds the bigger issue - that neither the driver nor station staff seemed aware of what was happening."
This situation could have ended in a tragedy (if he'd had a stronger rucksack that didn't break) and it's worrying to think that people can be dragged along the platform like this. Hopefully, Transport for London will be able to think of a better statement than not wanting to disrupt Northern Line passengers in the rush hour to collect the guy's belongings. I'd be interested to hear from any staff as to how the train was even able to go along any distance with the door partially open and a man hanging from it!