> Except the UK economy has been expanding for a long time now and it's still described as using austerity.
That's why I wrote that the UK was engaging in austerity. Past tense. Osborne abandoned austerity in 2012 (though the Cameron government's economic policymaking still does not show a clear strategy and the UK's economy is still pretty fragile [1]).
That the term "austerity" is sometimes used imprecisely (especially in colloquial speech) is not something I disagree with; however, austerity is not synonymous with having a balanced budget, as the OP claimed.
> Spending your way out of recession [in the midst of large pre-existing debt] has its own supporters and detractors. I've generally come to the conclusion that whatever your budgetary preference you can find an macro-economist to agree with you.
First, these are not the only two alternatives (fallacy of the excluded middle and all that). Second, critics of austerity do not rely on "finding a macro-economist to agree with them" but on the pretty clear evidence that at least for the ongoing crisis, austerity has been unsuccessful (change in government spending has been correlated with change in GDP; i.e., less government spending => less or negative GDP growth). In short, the hypothesis that austerity leads to GDP growth has so far been falsified by the evidence we have.
[1] Loss of real GDP and lower real wages compared to pre-crisis levels; a recovery largely fueled by consumption (in part, ironically, because of increased net migration to Britain) and rising housing prices, which is not sustainable in the long term.