One of Ed Miliband's boldest decisions since becoming Labour leader has been to target the coalition's welfare cuts and today's PMQs saw an all-out assault on the "bedroom tax [2]". For those unfamiliar with the term, it refers to the government's plan to cut housing benefit for those deemed to have more living space than they need, such as a spare bedroom. Social housing tenants with one extra room will lose 14 per cent of their benefit, while those with two or more will lose 25 per cent.  

The government argues that this is another necessary measure to reduce the ballooning housing benefit bill (which is largely due to extortionate rents and substandard wages) but Miliband highlighted the case of a mother with two sons in the army who would lose out while they were away "serving their country". He went on to warn that two-thirds of those affected are disabled (many of whom require an extra room due to their disability) and that it would encourage social housing tenants, "the most vulnerable", to move to the more expensive private sector, wiping out any savings from the policy as the housing benefit bill rises. Miliband also smartly contrasted the Tories' "bedroom tax" with their opposition to a "mansion tax", brandishing a letter from the party to Conservative donors asking them to contribute to a fighting fund against a "homes tax". 

Cameron gave little ground in response, pointing out that there was a £50m fund to deal with "difficullt cases" and bluntly asking why it was fair for social housing tenants to receive money for an extra room when private tenants did not. For a self-described "compassionate Conservative", it was a rather compassionless reply. As Cameron's answers became increasingly ill-tempered, Miliband deftly weaved in a reference to last night's vote on equal marriage: "He shouldn't get so het up. After all, he's got almost half his parliamentary party behind him." Unsurprisingly, the line went down well with both sides of the House. 

The PM's best moment came when he remarked of Miliband: "we know all the things he's against, we are beginning to wonder what on earth he's for?" If Labour is opposed to the "bedroom tax", the "strivers' tax", the "granny tax", the "toddler tax", how would it reduce public spending? Would it introduce a "mansion tax"? Miliband gave the stock reply that "the clue's in the title - Prime Minister's Questions - he's supposed to try and answer them". But this riposte, while acceptable in 2010, is less impressive halfway through the parliament, with Labour MPs increasingly troubled by the perceived lack of policy detail from their leader.

After Miliband had used up his six questions, Labour MPs continued to challenge Cameron over the "bedroom tax" in a well coordinated assault. An increasingly exasperated Cameron repeated that the "bedroom tax" was not a tax but, in doing so, he unwittingly repeated Labour's attack line. Whether the PM likes it or not, when voters hear him refer to the "bedroom tax" that is what they will call it. Across the floor, Miliband and Ed Balls smiled contentedly in response. Their work for the day was done.