Image copyright Getty Images Image caption Conservatives say the coalition's changes to benefits saved £21bn during the last Parliament

The UK spends about £220bn annually on social security payments. And most of that goes on pensioners.

The Conservatives have already pledged to protect pensioner benefits. So the party is focusing on £125bn of unprotected welfare spending, most of which goes to people of working age. That's the total bill they want to reduce by £12bn by 2017-18.

Cutting that sum within that timescale would be difficult and controversial, and could be made even harder by low inflation rates.

Take the main detail they've given us: freezing working-age benefits for two years. When Chancellor George Osborne announced that last year, he said it would save £3bn.

But inflation is now predicted to be much lower, so the Institute for Fiscal Studies - an independent think tank that analyses public spending - calculates the likely saving to be closer to £1bn.

So how else could you get to £12bn?

Leaked documents seen last month by the BBC suggested the Conservatives were considering options for scrapping several benefits, although the party insisted that while its officials had commissioned civil servants to draw up the proposals they were not policy.

'Way short'

Taxing disability benefits could save £1.5bn, cutting the contributory element of Employment and Support Allowance, the main sickness benefit, and Job Seekers Allowance would save about £1.3bn.

Changing who is eligible for carers allowance would save £1bn, and scrapping the Industrial Injuries Compensation Scheme would save a further £1bn. Now, if you did all that - which, it is important to stress, the Conservatives told us at the time was "not part of their plan" - you would save just £4.8bn.

Add in the measures they've announced - another £1bn - and you're still way short of the £12bn target.

Today we learned that officials at the Department for Work and Pensions will offer any incoming Tory ministers the option of scrapping child benefit for all but the poorest families.

The idea is to make it only eligible for those on Universal Credit, which would mean about two thirds of families who currently receive Child Benefit would lose out.

That single measure would save more than £4bn - getting you much closer to £12bn - but ultimately it would be up to the incoming ministers to decide whether to take that option.

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