The 54-year-old comedian told The Guardian: “Cake is so backward-looking, isn’t it?... I remember phoning Perks saying, ‘Don’t worry, mate – no one’s ever going to see this.’
"Because we were really scared. We were thinking, ‘Well, that’s the end of our careers. That was the flattest, twee-est, most boring thing we’ve ever done. Who wants to look at cakes?' ”
The baking competition went on to become a huge hit - and has won three TV Bafta Awards and five National Television Awards.
It began in 2010 on BBC Two, but due to its success was moved to BBC One in 2014 to air in a primetime slot.
Giedroyc said: "It was just mad. No one could have predicted that it would explode in that way – we certainly couldn’t have. What a joy to have that mad thing happen to you in your 40s. It just doesn’t happen to two old birds.”
In 2016 Bake Off makers Love Productions announced they had signed a deal with Channel 4 and would be leaving the BBC.
Giedroyc revealed she and Perkins were contacted by the head of C4 to say they hoped the comedy duo would continue to host the show.
She added: "I think it took us under 20 seconds to work out that we weren’t going to go with it. We felt that the show had been nurtured by the BBC. And effectively, the makers of the show were just going ‘See ya’, and going for the money. And that didn’t sit well with us.”
Judge Paul Hollywood remained a Bake Off judge and was joined by food writer Prue Leith. Comedians Sandi Toksvig and Noel Fielding took over hosting the show as part of the move to Channel 4.
Toksvig has now been replaced by Little Britain’s Matt Lucas.
Watch: Great British Bake Off 2022: Meet this year's bakers