NICK Clegg will defend the Coalition Government's controversial welfare reforms in a keynote speech today marking five years since he became Liberal Democrat leader.

The Deputy Prime Minister will insist changes to the benefits system are borne of "centre ground" politics.

The Conservative-LibDem administration has come under growing fire from campaigners, trade unionists and Labour and SNP politicians over reforms designed to slash £10 billion from the welfare budget.

Measures include tough assessments for disability benefits and cuts to payments for Jobseekers Allowance Claimants who refuse a "reasonable" work offer.

But Mr Clegg is expected to tell an audience in London: "Let's be honest – some people do need tough sanctions to get them active."

He will say that under Labour the benefits system was unfair and unaffordable and the Coalition had a social and financial duty to reform it.

He will defend the changes –developed by Work and Pensions Secretary and former Conservative leader Iain Duncan Smith –as "sensible, centre-ground welfare reform".

He will add: "Politicians of the centre ground, who believe in a benefit safety net, have an absolute duty to be tough on those few who abuse, or try to abuse, the generosity of tax payers and exploit our benefits system, and an absolute duty to make sure the system as a whole is – and appears to be – fair."

He adds: "Some of our critics believe either that the Liberal Democrats in government did not want to reform welfare or were powerless to stop the Conservatives from doing so.

"The truth is this: yes, welfare reform has been painful and controversial at times, but it was in our manifesto and on our agenda right from the start.

"The Liberal Democrats are now the party of welfare reform – sensible, centre-ground welfare reform." He insists: "I want us to keep at the front of our minds the idea that a liberal state is an enabling state."

Mr Clegg's comments come in a speech subtitled "building a stronger economy in a fairer society" – which is set to be the mantra of the LibDems from now until the 2015 General Election.

Details of Mr Clegg's speech were released on the day a new poll showed the LibDems had slipped behind UKIP.

The ComRes poll put UKIP on 14%, ahead of the LibDems on 9%. The Conservatives were on 28%, down three points and 11 points behind Labour, who are down four on 39%.

Mr Clegg will say the LibDems have remained in the centre ground of British politics and attack elements of both his Tory Coalition partners and the Labour opposition.

He will say the Tory right "dreams of a fantasy world" in which the UK quits the EU, while the Labour left "lives in a different, but no less destructive, fantasy world" of ruinously high Government borrowing.

But he will staunchly defend the need for his party to enter coalitions now and in future.

He will say: "If we are to become a more permanent fixture of government, then it will be, at least at first, as a partner in coalitions.

"That means embracing the realities of coalition government, and becoming better and better at negotiating successfully on behalf of those in Britain who expect us to stand up for them. It means accepting compromise."

He adds: "This is the lesson we've learnt in government. The challenges of governing at a difficult time have given us a harder edge and a more practical outlook."