As a fellow current Labour member (although not for all my life - I was a floating voter in 2010), I'll bite on that one.
Firstly, remember that the important figure is debt
as a % of GDP. (Because if you're earning £100K/year then a debt of £10K is much less significant than if you're earning just £10K/year).
You might be surprised to learn that until the 2008 recession struck, Gordon Brown
had by that measure reduced the debt - from 42% in 1997 to 39% in 2008. Figures
here. Obviously, the cost of preventing the recession from becoming a depression blew that out of the water, so in 2010 it was 64%. Under George Osborne, that has risen further to 75%.
Should Gordon Brown have done more to reduce it further? I don't think any of us here has enough expertise in economics to give a definite answer that question. My own view based on what economics I did learn is that, in an ideal world, it would have been desirable for him to do so, but that it was hardly the most important issue in the world. As far as I'm aware, debt levels until 2008 were not historically unusual, and I'm not aware of any significant mainstream economic thought that
at the time (ie. not with the benefit of hindsight) said those levels were bad for the economy, so the fact that he didn't prioritise it at the time doesn't really
by itself say anything bad about him or about the Labour Government.
The Conservatives, helped by much of the media, have elevated the issue of the debt in public consciousness to a much higher importance than is justified by its real importance in the economy - and I assume that for the Conservatives, this is in part motivated by the convenience for their ideology, since they are clearly committed to small Government for reasons that are purely ideological (ie. not based on practicalities or on any rational assessment of what actually works). The convenience for that ideology of seeking to convince people that there are economic reasons for spending less should be obvious.
In reality, issues of investing in our ability to produce goods, in infrastructure, etc., and of ensuring we have a diverse healthy economy and society go way, way, beyond how high Government debt is. The danger is that, by making out as the Conservatives do, that clearing our debt is the most important thing, we could end up sacrificing other things that are actually far more important in sustaining healthy economic growth, and thereby doing more harm than good. But, as I say, if it was possible to reduce the debt without affecting other things, then ideally, yes, it would have been better to do so.
But as I say, that's my best assessment based on not being an expert in economics. If someone came along who genuinely is a professional with expert knowledge, then I'd probably defer to their opinion