Where I struggle though is at a more macro level. Apart from consumption (which I think can be at least partly explained by the fact that people are trying to deleverage their enormous household debts) the sluggish GDP growth can be put down to three principal causes: diminished production of North Sea oil and gas; depressed activity in the financial sector, and huge falls in construction.
These are all principally supply-side problems, and demand-side measures (like fiscal policy) aren't really going to sort them out. By way of illustration - there's no shortage of demand for houses in most of the UK. Problems in the construction sector must therefore be on the supply-side. I can envisage Government led solutions to this (planning reform, planning reform, planning reform) but I don't really see that an increased deficit is the most efficient way to deal with it.
Similarly with the financial sector, much of the fall in activity has been the equivalent of blowing the froth of a cappuccino. As such it's a decline in illusory production (and has indeed been partly policy-led). This surely isn't a failure than needs to be (or could be) corrected by greater public spending.
As to oil and gas - much of the fall in production is the inevitable result of an ageing oil field with diminishing reserves. More is the result of catastrophically short-sighted tax policies initiated by Gordon Brown and exacerbated by George Osborne (marginal tax rates on some fields are now as high as 81%). When you tax something, you get less of it. When you tax something punitively, you get much less of it. Here at least is a candidate for Government intervention, if only by cutting rates.
However, for all three sectors, there are signs of good times ahead. For oil and gas, capital investment is at an all time high, and production is forecast to start rising again. For the financial sector, the recapitalised banks are returning to profitability. Even construction is showing signs of stabilising. I'm not sure that any of these are really determined by fiscal policy. Austerity didn't cause their decline, and stimulus wouldn't trigger their recovery. I sometimes get the feeling that the policy battles over austerity vs stimulus are really a proxy for something else.