There's more than a dash of Brownite politics about this - the same seasoning I detected in the Tories' Death Tax poster. Sure, there have been rumblings that the Tories will raise VAT. But Osborne & Co. have denied that this is necessarily the case in recent days, and it's certainly not current Tory policy. So the Lib Dems are effectively spinning a lie, and attacking that lie.
You could say that that's what election campaigns are all about. That we've got to expect a little bit of rough 'n' tumble. But I still find it kinda dispiriting.