By David Milliken and Peter Griffiths

LONDON, Dec 5 (Reuters) - Britain will endure more austerity

and break a central debt-cutting promise to cope with weaker

growth, the government said on Wednesday, in a bleak outlook

that will do nothing to improve Prime Minister David Cameron's

re-election chances.

Finance minister George Osborne announced real-terms welfare

cuts and said tax rises and spending cuts will drag on for

another year into 2017/18 as Britain is held back by the euro

zone debt crisis and a global slowdown.

In a half-yearly budget update to parliament, Osborne said

weak growth meant he would be a year late in meeting a

self-imposed target of seeing debt fall as a share of Britain's

national income by 2015/16.

Missing that goal is an embarrassment for Osborne, who has

staked his reputation on wiping out Britain's deficit and

cutting public debt. It also raises questions about the safety

of Britain's coveted triple-A credit rating.

The opposition Labour Party -- which leads Cameron's

Conservatives by around 10 points in the polls, 2-1/2 years

before a 2015 election -- said the austerity drive had failed

and was holding back Britain's recovery.

But Osborne said he would not abandon the government's

flagship policy.

'Britain is on the right track. Turning back now would be

disaster,' Osborne told parliament to roars of disapproval from

opposition politicians. 'It is a hard road, but we are getting

there.'

The economy was now forecast to grow by only 1.2 percent in

2013, well down from the 2 percent predicted in March, Osborne

said, citing figures from the independent Office for Budget

Responsibility.

The government's fiscal watchdog expected the economy to

shrink by 0.1 percent in 2012, compared to a prediction of 0.8

growth in March, and grow by 2 percent in 2014, compared to the

2.7 percent previously forecast.

'We suspect the risks to the growth forecasts are slanted to

the downside, particularly from 2014 onwards, and that this

poses an appreciable risk to the government's new fiscal

targets,' said Howard Archer, economist at IHS Global Insight.

'This could make life difficult and complicated for the

government just ahead of the general election that is due by May

2015.'

Although Wednesday's OBR forecasts showed Osborne was set to

miss his debt reduction goals, there was less slippage than many

economists had expected.

And his primary goal of bringing Britain's structural

current budget into balance is still on track to be met in the

2016/17 tax year -- in contrast to widespread expectations that

this would get pushed back to 2017/18.

But a sluggish economy has wrecked the Conservative-Liberal

Democrat coalition's original plan to wipe out a large

structural deficit before the next election due in 2015.

The government made dealing with Britain's budget deficit --

which hit a record 11.2 percent of GDP before the 2010 election

-- its biggest priority when it came to power.

Osborne told parliament that Britain's deficit would fall

every year until the next election, adding: 'Yes the deficit is

still far too high for comfort. We cannot relax our efforts.'

LABOUR ON ATTACK

Labour accused Osborne of stubbornly sticking to a failed

austerity plan that has choked off growth, sapped demand and

eroded much-needed tax revenues.

'Today after 2-1/2 years we can see, and people can feel in

the country, the true scale of this government's economic

failure,' Labour finance spokesman Ed Balls told parliament.

Balls asked if the euro zone was such a drag on the UK's

recovery, why had the currency area grown faster than Britain.

'It is simply reckless and deeply irresponsible of this

Chancellor to plough on with a fiscal plan we all know is

failing on the terms he set,' he said.

The government's watchdog said 1.1 million public sector

jobs would be lost by 2018 because of further spending cuts in

2017-18. The Trades Union Congress said Osborne had offered

'pain without purpose'.

Cameron has had a bruising year marked by weak growth,

criticism of his austerity measures and an unpopular budget in

March that led to a series of policy U-turns.

Osborne says he had no choice but to deal with a record

budget deficit left by the last Labour government, which was

voted out in 2010. As a result, he said investors still flocked

to the British government bond market, keeping borrowing costs

at record lows.

Nonetheless, Britain could be in danger of losing its prized

triple-A credit rating before long.

'Fiscal slippage is creeping in. The question is 'How will

the ratings agencies take this?',' said Peter Dixon, an

economist at Commerzbank. 'His fiscal strategy is sailing very

close to the rocks.'

In a raft of announcements, Osborne said he would consult on

new tax incentives for the shale gas industry, extend a

high-speed rail line into northwest England and launch a new 1.5

billion pound finance facility to support UK exports.

Under pressure to do more to restore growth, he said he

would cut the main rate of corporation tax by a further 1

percent. It will stand at 21 percent from April 2014.

Banks will not benefit, however, as a levy on their balance

sheets will rise to 0.130 percent to offset any benefit. And

unemployment benefit will only rise by 1 percent a year for the

next three years, rather than the normal inflation-linked rise.

In total, the measures were 'fiscally neutral', Osborne

said, neither pushing money into nor taking it out of the

economy.

($1 = 0.6209 British pounds)

(Additional reporting by Matt Falloon, Peter Schwartzstein,

Kate Holton, Michael Holden, Estelle Shirbon and Jonathan Cable.

Editing by Guy Faulconbridge and Mike Peacock)

Keywords: BRITAIN ECONOMY/

(peter.griffiths@thomsonreuters.com)(+44 7542 6701)(Reuters Messaging: peter.griffiths.thomsonreuters.com@thomsonreuters.net)

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