Will welfare cap vote be Miliband's biggest rebellion?

So Rachel Reeves confirmed in the Commons today that Labour will back the welfare cap when it comes to a vote. Tory MPs cheered her as she announced this.

There is a rebellion brewing on the Labour benches on this, which party sources are saying they remain ‘vigilant’ about. Some claim that this will be the biggest revolt of Miliband’s leadership. If it is, then it will have to surpass the 40 Labour MPs (39 and one teller) who rebelled against their party’s official position on welfare sanctions just over a year ago. The then Shadow Work and Pensions Secretary Liam Byrne instructed Labour MPs to abstain on a bill which enabled the DWP to avoid repaying benefits to people sanctioned for refusing to take part in the government’s work experience programme. But those 40 MPs chose to vote against the emergency legislation.