With both Labour and the Lib Dems no longer committed to preserving universal benefits for pensioners, what's preventing the Tories executing their own U-turn? The answer is David Cameron's 2010 "read my lips" pledge  to protect them (ironically made under pressure from Labour), which was subsequently included in the Coalition Agreement. After seeing the damage inflicted on the Lib Dems by their volte face over tuition fees, Cameron is determined to avoid anything that could provoke claims of betrayal, not least due to the renowned power of the grey vote (the demographic among which UKIP is performing strongest).
But as Nick Clegg pointed out  on The Andrew Marr Show yesterday, the coalition's pledge to "protect key benefits for older people such as the winter fuel allowance, free TV licences, free bus travel, and free eye tests and prescriptions" only applies up to May 2015, while the current Spending Review is concerned with the 2015-16 spending period. The difficulty for Cameron is that six weeks of the period fall before the next general election, meaning any decision to means-test them would technically breach his pledge. As a result, Tory hopes of further welfare cuts, which would allow the government to limit cuts to areas such as policing and defence, have evaporated. As Clegg again stated yesterday, he is only prepared to consider additional cuts (such as the abolition of housing benefit for 25-year-olds and the limiting of child benefit to two children) if the coalition "starts at the top" by curbing benefits for the wealthy. In response, the Tories reaffirmed Cameron's 2010 pledge: "David Cameron promised to protect the benefits for pensioners who've worked hard and done the right thing - and we've kept that promise. Conservatives want to do more to fix the welfare system so that it works for the hard-working people who pay for it."
But with the Treasury still only a third  of the way to meeting its Spending Review target of £11.5bn cuts (a total that will be far harder to reach with welfare cuts off the table), it's worth noting one way the coalition could resolve this conundrum. The government could announce that one or more of the benefits will be means-tested from April 2015 and increase payments to pensioners the previous year to ensure no one is left out of pocket. While administratively complex, this would offer the coalition a chance to break the deadlock on welfare. As Philip Hammond, Vince Cable and others battle to protect their departments from the full force of Osborne's axe, it's exactly the kind of imaginative compromise both sides might be tempted to explore.