It caps a remarkable turnaround for the Brunton Park side, who were relegated out of the Football League two seasons ago - when Scunthorpe narrowly beat them to safety.
They bounced back at the first opportunity, winning the Conference play-offs last season, and will compete in League One next year.
Simpson said: "We need to get ourselves straight again after a couple of days because we want to make sure that we finish top. But we are going to enjoy the moment.
"It is a great reward for two-and-a-half years' hard work, and it's what we
have all wanted at the club.
"This tops everything that we have achieved so far, and no-one would have
expected this to have happened when I first came to the club."