LONDON (Reuters) - Britain's trades unions will launch a campaign next week to persuade voters to oppose massive public spending cuts, although commentators say their power to sway the government is limited.
The Conservative-Liberal Democrat coalition, which took power in May, plans to cut spending by 25 percent in many departments to tame a budget deficit totalling 11 percent of national output.
The unions, which hold their annual conference in the northern city of Manchester next week, fear the cuts will mean hundreds of thousands of job losses in the public sector.
They hope to start to build momentum towards a mass rally outside parliament in London on October 19, the eve of the announcement of the spending programme for the next four years.
Unions are flexing their muscles across Europe as governments seek to restore order to public finances following the ravages of the global credit crisis, but have had little success so far in resisting austerity measures.
Brendan Barber, general secretary of the Trades Union Congress (TUC), has drawn parallels with protests in 1990 against the "poll tax" -- a local levy that sparked riots in London and was eventually replaced.
"The poll tax was defeated when government MPs returned to Westminster to report that their constituencies were in revolt. The poll tax offended the British people's basic sense of what's fair. So will the spending cuts," Barber said this week.
"Every coalition MP with a small majority and every coalition MP who fought an election to oppose deep early cuts needs to feel the pressure from their constituents to change course," he added.
The TUC argues that cutting spending too quickly will plunge the country back into recession.
Its delegates will get an expert view on the economic situation because the governor of the Bank of England, Mervyn King, will deliver a keynote speech on Wednesday, filling a slot usually reserved for a senior government figure.
Union membership has halved since the end of the 1970s but the TUC still has 6.5 million members, many of them in the public sector.
Business Secretary Vince Cable has said that the government is not looking for confrontation with the unions and warned them that hardline tactics could backfire.
He cited the example of the 1978-79 "Winter of Discontent" when unions staged widespread stoppages, helping to bring Margaret Thatcher's Conservatives to power.
"It also undermined public support for the trade union movement and opened the way to the Thatcher reforms of trade unions, which greatly weakened them," Cable told the New Statesman this week.
"This government is not looking for conflict of that kind."
Analysts said union protests had the power to discomfort the government but not make it change course.
"The days when the unions could hold the government to ransom in any serious and long-term way are behind us -- but that's not to say there couldn't be some incredibly serious disruption," said Justin Fisher, a political analyst at Brunel University in southern England.
"It will be unpleasant, I assume, but not threatening to the government."
Additional reporting by Matt Falloon; editing by Paul Taylor