The 'True' singer wanted to reform the pop group, who split in 1989, when offered the opportunity because he thought at 49 he wouldn't get the chance again.
He said: "There was a massive groundswell of desire from the fans and I thought, well, this is bigger than us.
"I'm pushing 50. I just thought, 'What if it never happens again?' It's not about the money."
Tony also revealed he and his bandmates - who were embroiled in an acrimonious royalty battle in 1999 - made the decision to reform in a pub.
The frontman - who is joined in Spandau Ballet by Gary Kemp, Martin Kemp, Steve Norman and John Keeble - added: "After a few beers, all the old jokes and stories we'd shared came out again. So, yeah, there were a few laughs. And we also said the tough stuff we had to say. There were some 'sorrys', too. It was horrible at first, of course."