This is the new dark arts of politics. Rather than saying what they intend to do, each side claims what they think the other might be intending to do. Both sides can then deny what the other says they are going to do as idle speculation (i.e. "nonsense") on the part of the other, thereby committing to nothing and leaving the voter thoroughly confused as to who is promising what in a race to the bottom to determine which of the parties is most best least worst, when they're probably evens.
Expect a Tory campaign based on "what Labour will blow big sums of money on" with a Labour response of "we're going to cut just as much as the Tories, but in a different way and a Labour campaign based on "we're not them, honest, although we're basically promising to spend the same way they do". And a Libdem campaign of "Please, for the love of God, please vote for us! We can change, we'll try harder. We're not like that lot! Don't go, we need these seats - we've got second mortgages to pay for! Policies? Oh we'll do pretty much the same as the other lot, but we'll do it in a fairer way"
There was a short Adam Curtis piece on this in 2014 Wipe.