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By Adrian Croft

BASRA, Iraq, Dec 9 (Reuters) - British Prime Minister Gordon Brown made an unannounced visit to Iraq on Sunday and said his country would hand responsibility for the last province it controls to Iraqi security forces within weeks.

After nearly five years, Brown is winding down Britain's mission in support of the U.S.-led war in Iraq.

His brief stop at an air base outside the southern city of Basra marked Brown's second visit to British forces here since taking over from Tony Blair as prime minister in June, a period that has seen his popularity at home tumble.

He praised the troops for contributing to Iraq's security. But in a sign of how precarious Britain's dwindling presence has become, journalists travelling with Brown were not allowed to report his visit until he was safely out of the country.

Britain now has about 4,500 troops in Iraq -- a tenth the force that Blair dispatched to help topple Saddam Hussein in 2003 -- and Brown has said that number will fall to 2,500 by mid-2008, mainly training Iraqis and guarding the base.

Brown is keen to demonstrate his commitment to Britain's armed forces after stinging criticism from ex-commanders and the opposition Conservatives, who accuse him of failing to provide adequate equipment, training and health care for British troops.

"I have just talked to Prime Minister (Nuri al-) Maliki. He asked me to pass on his thanks to you for what you've done to help rebuild the democracy of Iraq," Brown told a gathering of troops at the base after arriving in darkness after sundown.

"The reason why security is so much better here, the reason why things have improved, is because of you, because of what you've achieved," Brown said.

Brown, who spoke to Maliki by telephone, said the Iraqi leader had recommended holding the security handover of Basra province within two weeks.

Maliki's office said in a statement that Iraq was ready to take control of the vital oil producing province.

WITHDRAWAL FROM BASE

Britain has already handed over responsibility for security in three other southern provinces, and moved the last of its soldiers out of a palace in the centre of Basra to the air base on its outskirts in September, ending regular street patrols.

Britain has been winding down its Iraq mission even as Washington dispatched 30,000 additional troops this year.

Brown, 56, is keen to dissociate himself from Blair's Iraq policy which had become an electoral millstone. He has instead emphasised Britain's military role in Afghanistan, a mission that has grown even as the Iraq mission shrinks.

The two wars have stretched Britain's military, and a perception that Brown did not provide enough resources to fight them has led to unprecedented criticism from former top brass. Brown served as Blair's finance minister for a decade.

Last month five retired defence chiefs accused the government of neglecting the armed forces and risking soldiers' lives. Some of the attacks, delivered in robust speeches in the House of Lords, were aimed personally at Brown.

On his last trip to Basra in October, Brown said 1,000 British troops would be home from the unpopular war in Iraq by Christmas. But that visit backfired when it emerged that hundreds of them had in fact already left.

Critics accused him of using the visit to distract attention from the opposition Conservatives' annual conference and to lay the ground for a possible early election. Brown's poll ratings tumbled and within days he cancelled the election plans.

Since then, his political fortunes have further slumped amid scandals over secret party donations and missing computer discs containing personal details of 25 million Britons.

(Editing by Peter Graff and Dean Yates in Baghdad)

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