The latest national accounts data we have is for 2013 Q3. Between 2012Q4 and 2013Q3 real GDP increased by 2.1% (actual, not annual rate). Not a great number, but it represented three continuous quarters of solid growth, which we had not seen since 2007. So where did this growth come from? The good news is that investment over that same period rose by 4%. (This and all subsequent figures are the actual 2013Q3/2012Q4 percentage growth rate.) Business investment increased (2.7%), public investment did not (0.5%), but dwellings investment rose by 8%. The bad news is that exports rose by only 0.1%. Government consumption increased by 1.0%.
Over half of the increase in GDP was down to a 1.8% rise in consumption. Not huge, but significant because it represented a large fall in the savings ratio, as this chart shows.
The large increase in saving since 2009 is a major factor behind the recession. The recovery this year is in large part because the savings ratio has begun to fall. We should be cautious here, because data on the savings ratio is notoriously subject to revision. However if we look at the main component of income, compensation of employees, this rose by 3.4%, while nominal consumption rose by 4.4%, again indicating a reduction in savings.
So the recovery so far is essentially down to less saving/more borrowing, with a minor contribution from investment in dwellings (house building). As Duncan Weldon suggests, the Funding for Lending scheme may be an important factor here. However it may also just be the coming to an end of a balance sheet adjustment, with consumers getting their debts and savings nearer a place they want them to be following the financial crash.
I cannot help but repeat an observation that I have made before at this point. Macro gets blamed for not foreseeing the financial crisis, although I suspect if most macroeconomists had seen this data before the crash they would have become pretty worried. But what macro can certainly be blamed for is not having much clue about the proportion of consumers who are subject to credit constraints, and for those who are not, what determines their precautionary savings: see this post for more. This is why no one really knew when the savings ratio would start coming down, and no one really knows when this will stop.
Some people have argued that we should be suspicious about this recovery, because it involves consumers saving less and borrowing more. Some of the fears behind this are real. One fear is that, encouraged by Help to Buy, the housing market will see a new bubble, and many people will get burned as a result. Another is that some households will erroneously believe that ultra low interest rates are here forever, and will not be able to cope when they rise. But although these are legitimate concerns, which macroprudential policy should try and tackle, the truth is that one of the key ways that monetary policy expands the economy is by getting people to spend more and save less. So if we want a recovery, and the government does not allow itself fiscal stimulus, and Europe remains depressed because of austerity, this was always going to be how it happens. 
However there is a legitimate point about a recovery that comes from a falling savings ratio which is that the savings ratio cannot go on falling forever. The moment it stops falling, consumption growth will match income growth. The hope must be that it will continue for long enough to get business investment rising more rapidly, and for the Eurozone to start growing again so that exports can start increasing. But the big unknown remains productivity. So far, the upturn in growth does not seem to have been accompanied by an upturn in productivity. In the short term that is good because it reduces unemployment, but if it continues it will mean real wages will not increase by much, which in turn will mean at some point consumption growth will slow.
There is a great set of graphs in this post at Flip Chart Fairy Tales which illustrate the scale of the productivity problem. (Rick - apologies for not discovering your blog earlier.) For example the OBR, in November 2010, were expecting real wages in 2015 to be 10% higher than in their recent Autumn Statement forecast. We will not recover the ground lost as a result of the recession until productivity growth starts exceeding pre-recession averages. As Martin Wolf and I suggest, the Chancellor should be focusing on the reasons for the UK’s productivity slowdown rather than obsessing about the government’s budget deficit.
 In theory it could have happened through a large increase in investment. However the experience of the recession itself, and more general evidence, suggests that investment is strongly influenced by output growth. That is why investment has not forged ahead as a result of low interest rates, and why firms continue to say that a shortage of finance is not holding them back. Having said that, I would have prefered the government to try fiscal incentives to bring forward investment rather than implement measures aimed at raising house prices.