The UK must restore its reputation in the world, Deputy Prime Minister Nick Clegg is expected to tell the UN general assembly in New York later.
He will say that tolerance and fairness are in Britain’s “national DNA”.
But he will add the UK has learned “the hard way” that democracy “cannot be created by diktat”, in comments likely to seen as a reference to the Iraq war.
He will also say the UN needs a “radical overhaul” to tackle the international challenges it faces.
Mr Clegg will tell the UN: “Britain will stand as a beacon of democracy, freedom and law.
“Many of the values that must be at the heart of a new global settlement are in our national DNA – tolerance, fairness, democracy, equality before the law.
“Too many nations and international institutions have been too reticent about promoting enlightened, human values”
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“But our approach will also be hard-headed and realistic. In recent years, we have learned – sometimes the hard way – that democracy cannot be created by diktat. Freedom cannot be commanded into existence.
“The new coalition government, now five months old, will restore Britain’s international reputation by pursuing a hard-headed foreign policy based on liberal values.”
Although Mr Clegg may not refer to Iraq directly in his UN speech, earlier this year he described the 2003 invasion of Iraq as “illegal”.
He made the statement in the House of Commons and was later forced to clarify that it was a personal opinion.
Mr Clegg will say taking action on international challenges requires multilateral co-operation, but a “radical overhaul” of the UN is needed to achieve those ends.
He will call for the expansion of the UN Security Council with permanent seats for Brazil, India, Germany and Japan, as well as representation for Africa.
Mr Clegg will say the financial crisis, along with the collapse of the climate change talks in Copenhagen and the stalling of the Doha trade round, has put in question the effectiveness of multilateral approaches.
“Too many nations and international institutions have been too reticent about promoting enlightened, human values,” he will say.
“We need to inject new life into our institutions, and new confidence into the expression of our ideals. Reform is essential.”
Mr Clegg will also call for strong political leadership on Afghanistan and the Middle East peace process, and for the UN to improve its response to what he will describe as the “outrageous abuse of democracy” in Burma.
On Thursday, Mr Clegg travelled to Washington for talks at the White House with US Vice-President Joe Biden.
They were said to have discussed Afghanistan, UK and US domestic policies, and the floods in Afghanistan.
A spokesman for Mr Clegg said the meeting, which lasted more than two hours, was “warm and productive”.
The talks had been due to finish much earlier, so much so that Mr Clegg missed a scheduled appointment with Senator John Kerry, chairman of the US Senate’s foreign relations committee.
Speaking before the meeting, Mr Clegg said the two nations had a “terrifically important relationship”.
“It ebbs and flows over time but it is hugely important and it is built to last.”
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