Stewards for the race at Aintree issued a report stating 39 of the 40 jockeys had disobeyed orders ahead of the start, resulting in the assistant starter being knocked to the ground.
After a false start, the race was able to get underway at the second attempt with Pineau De Re taking victory by five lengths from Balthazar King and Double Seven.
A stewards' inquiry was called following the race in order to allow the jockeys to explain why they had approached the starting tape before being invited to do so.
However, the jockeys refused to return to the stewards' room, and the matter has been referred to the BHA, who have confirmed they will undertake be a full investigation.
"An inquiry into the start of the Grand National was referred on to the British Horseracing Authority after jockeys chose not to participate in the on-course hearing," a statement read on their website.
"After taking initial evidence from the riders and the starting team, the stewards adjourned the inquiry to consider the matter.
"The report said that in attempting to reconvene the inquiry after the last race, the riders, who had not been given permission to leave the course, refused to attend the inquiry."
Only Brendan Powell, who rode Battle Group, was not involved after his horse refused to approach the start.