Oh well, if the Beeb says it then it must be true!
But it's not in his famous and possibly history-changing speech last September:http://www.cityam.com/1411051570/gordon-browns-better-together-speech-eve-scottish-independence-referendum-vote-full-video
...... so when did he say it?
Incidentally, it's worth watching a bit of that, if only to admire the rhetorical style of his delivery, the effective speaking from memory (think Ed Miliband!), and the unashamed appeal to the emotions. Most politicians don't speak like that nowadays - it's a world away from Barack Obama, or David Cameron, both of whom I regard as excellent speakers, but times and styles have changed so much.