Talk Elections

What's different between 1992-present if Gordon Brown was to become Labour leader in 1992 after the party lost?

You probably mean 1994, right?  In OTL, John Smith was elected Labour leader in 1992, and died of a heart attack in '94.  That's when Blair was elected and Brown agreed not to run against him.  If Brown had been elected leader, Labour still would've probably won, perhaps by a slightly smaller margin.  
1994-Gordon Brown elected Labour leader.
1997-Gordon Brown leads Labour to a landslide victory in the general election with about 40% of the vote, compared with 32% for the Conservatives and 19% for the LibDems.  Brown's form of social democracy is less market-oriented than Blair's in OTL, though it's still a far cry from "Old Labour." Soon after the new government comes into office, Chancellor Tony Blair announces, abruptly, that he's privatizing the Bank of England.  Gordon Brown is furious, but he decides not to sack him.
2001: The Labour government is returned to power, albeit with a reduced majority.  
2003-After years of stopping Blair from pursuing a market-driven, Thatcherite agenda, and keeping him as Chancellor for the sake of party unity, Brown reeches the end of his patience with Blair.  After Brown refuses to back George Bush's war in Iraq, Blair publicly criticizes him for "failing to live up to the fight against terrorism." He challenges Brown for the leadership, and looses, resulting in a life on the backbenches.
2005-While the majority of Brits approve of the war at the time (resulting in a brief Conservative poll lead), Labour regains a lead in the polls and wins the 2005 election by a landslide bigger than they did in 1997 (more like '97 in OTL) due to a perception that Brown did the right thing in spite of it going against public opinion at the time.
2009-At general election of 2009 (due to not having had a leadership change) Labour looses its majority due to the economy, and has to govern with the Liberal Democrats in a coalition.