Britain's Miliband seeks to bolster economic credentials in bid to win power

(Adds YouGov opinion poll, changes date)

By William James

LONDON, April 13 (Reuters) - Britain's opposition Labour leader Ed Miliband will seek to allay concerns about his party's economic competence by unveiling a manifesto on Monday that pledges to protect the national finances and end tax avoidance by the rich.

In a bid to edge ahead of Prime Minister David Cameron's Conservatives in what polls indicate is the closest British election of recent times, Miliband will pledge to build a fairer society if he is elected prime minister on May 7.

At stake is more than simply who shall govern the $2.8 trillion economy: Cameron has promised a referendum on European Union membership while Scottish nationalists, who want Scotland's independence, are seeking a kingmaker position.

Pitched as a manifesto for "the working people of Britain", Miliband will unveil his shop window of election promises in Manchester, a party stronghold in the north of England.

"My case is simple: Britain can be better - for you, your family and our country," Miliband, 45, will say according to advance extracts supplied by the Labour Party.

"But only if we change the rules by which the country is run, the ethic that drives government, the leadership we offer."

At the heart of Miliband's election offering is an explicit challenge to what he says is Britain's unfair institutional bias towards large corporations and the wealthy at the expense of ordinary working families.

In an effort to stem criticism from the Conservatives, who enjoy higher opinion poll ratings for economic competence, Labour said funding for every pledge in the manifesto had been clearly set out and none would require extra borrowing.

Labour said it would to reduce the budget deficit each year.

The party's fiscal aim, to balance the books by 2020 at the latest, is looser than that set by the Conservatives, who want to run a surplus by 2018/19.

The Conservatives have focused on Labour's economic record during the campaign. Cameron says Labour, in power from 1997 to 2010, a period which included the 2008 financial crisis, left the country almost bankrupt with Britain's biggest peacetime deficit.

'TEAR UP ASSUMPTIONS'

The son of a Belgian Marxist intellectual of Polish origin, Miliband won the Labour leadership in 2010 after defeating his brother David, the early favourite.

In a newspaper interview on Sunday, Ed Miliband compared himself to previous Labour prime ministers such as Clement Attlee, Harold Wilson and Tony Blair, who he said had each changed the way Britain was run.

"We're going to tear up the old assumptions," Miliband said.

Labour's finance minister in waiting, Ed Balls, has pledged to target rules on private equity firms and hedge funds, increase fines for those found to be in breach of the rules, and give tax authorities new powers.

Miliband's manifesto will also contain previously announced plans to end big firms' dominance of the energy sector and pay for a tax cut for smaller firms by scrapping a planned reduction in the rate of corporation tax.

Cameron will launch his party's manifesto on Tuesday, setting out a starkly different vision, prioritising a smaller state and economic strength through a plan to balance the country's books and pay its national debt without raising taxes.

Despite the fanfare of manifesto launches, most opinion polls show Labour and the Conservatives neck-and-neck with neither party likely to win an outright majority in the 650-seat Westminster parliament.

A YouGov (LSE: YOU.L - news) poll published late on Sunday showed Labour on 36 percent of the vote, 3 percentage points ahead of the Conservatives. A similar YouGov poll published a day earlier had both parties level on 34 percent.

In such a situation, Cameron or Miliband would have to trade with smaller parties such as the Scottish National Party, the Liberal Democrats, Northern Ireland's Democratic Unionist Party and the UK Independence Party to form a durable government. (Editing by Guy Faulconbridge)