* Gordon Brown takes on bigger role in Scottish vote
* Brown tells Scots: Stay in the United Kingdom
* Brown says Scotland will get more autonomy
* Brown courts Scots with social justice, welfare (Recasts, adds quotes, detail and colour)
By Alistair Smout
GLASGOW, Scotland, June 3 (Reuters) - Former British Prime Minister Gordon Brown sought on Tuesday to tempt Scots away from voting for independence by pitching the United Kingdom as the best vehicle to promote social justice and preserve welfare spending.
Striking a distinctly more positive tone than the British government which has warned Scots of the economic dangers of breaking the 307-year union, Brown said Scotland would win more powers and prosper if it stayed inside the United Kingdom.
In a passionate speech which signals the Scottish-born former Labour leader will play a more prominent role in the unionist campaign, Brown told Scots that voting against independence in a Sept. 18 referendum was the best way to guarantee their cherished state-funded welfare system.
"I'm asking you to vote 'No', because I'm asking you to cast a vote for social justice," Brown, who served as Britain's prime minister from 2007 to 2010, told activists in Glasgow, a Scottish city 340 miles (550 km) north of London.
"Social justice is not advanced by retreating into independence," said Brown, who cautioned that "inequality would last until doomsday," under the plans of Scottish nationalists who favour independence.
Polls show Scots are unlikely to vote to break the union, with roughly 40 percent against independence and 30 percent in favour. But there are still enough undecided Scots to swing the vote.
Since losing power in the wake of the financial crisis, Brown has kept a low profile in British politics but his intervention in the Scottish independence campaign is significant as he garners deep respect across Scotland.
Conservative Prime Minister David Cameron has conceded that his own privileged background and centre-right politics mean he isn't the best person to win over Scots who elected just one Conservative lawmaker in the 2010 national election.
Labour was the major party in the devolved Scottish parliament until it was beaten by the Scottish National Party in 2007.
Nationalist leader Alex Salmond says Scotland has suffered centuries of mismanagement by far-off leaders in London and that independence plus control of a share of Britain's North Sea oil would place Scotland among the world's richest countries.
Brown argued the Scottish National Party's commitment to cut corporation tax, as well as their refusal to tax higher earners more, was evidence that an independent Scotland would be less equal as an independent country.
"If you don't support raising taxes on income, or raising taxes on wealth, if you don't support any form of redistribution, how can you say you want to create a more equal Scotland?" Brown asked.
Speaking before a giant red poster which read "I'm voting NO", Brown was confident and relaxed on stage, in sharp contrast to his reputation as a prime minister with a fearsome temper.
The 63-year-old even quipped that the main difference between the Scottish independence debate and being prime minister was that he was enjoying this campaign.
But he also steered clear of the main anti-secessionist warning put forward by senior British politicians: Scotland's risk of losing of the pound.
Brown was quoted by a local Scottish newspaper as saying that the British government's anti-secessionist campaign had been too negative and risked alienating some Scots.
"The way the currency argument was put by the government made the issue Scotland versus Britain," Brown was quoted as saying in an interview with the Daily Record newspaper.
"It is bound to make people feel that people are talking down to us or are not taking us seriously or are trying to bully us." (Editing by Guy Faulconbridge)