Well both parties and everyone else present or in the general vicinity seem to be stating it is entirely fabricated. I suspect Milliband is just trying to spin it for his own/Labour's gain, as one would expect. The angle others have suggested upthread that this is a deliberate Tory propaganda strategy is interesting, and if true may be something that could backfire rather spectacularly IMO.
I was always expecting this election to be negative and dirty as neither major party has anything credible, new or of any remote value to offer, but I wasn't expecting quite this degree of manipulation and deliberate deception. I find it amuzing as neither Conservative or Labour can drop any in my estimation, they are already as low as it gets, but watching them scrape the barrel so hard already is nonetheless entertaining. Every little lie or smear from either side is hopefully another nail in the coffin of the two-party FPTP charade.