A recent speech by Andy Haldane, the Bank of England's chief economist, sheds a good deal of light on the cost of living crisis and the union-led "Britain Needs a Payrise" campaign. Haldane points out how grim the recent situation has been for real wages in the UK economy:

Growth in real wages has been negative for all bar three of the past 74 months. The cumulative fall in real wages since their pre-recession peak is around 10%. As best we can tell, the length and depth of this fall is unprecedented since at least the mid-1800s.

But is this because employers have suddenly become selfish capitalists, whereas before they were paying workers out of the good of their heart? Or is something else at play?

Productivity – GDP per hour worked – was broadly unchanged in the year to 2014 Q2, leaving it around 15% below its pre-crisis trend level. The level of productivity is no higher than it was six years ago. This is the so-called “productivity puzzle”. Productivity has not flat-lined for that long in any period since the 1880s, other than following demobilisation after the World Wars.

We usually think that wages and productivity will be pretty closely related. Employers are unlikely to consistently pay above productivity, because they'd lose money. But equally, they'll be unable to consistently pay far below productivity (less the share needed to rent the capital involved) because in a reasonably competitive market firms will compete their workers away with more attractive job offers.

We might think this is particularly true at the low wage end of the market, because much less of low-skilled workers productivity is job specific. An accountant makes a very poor lawyer, and a civil engineer is not qualified to write code, but a worker in McDonalds will be similarly good at Burger King, or for that matter Waterstones, JR Wetherspoon, Lidl or most other relatively low-skilled areas.

So basic economic models suggest pay will track productivity. And what do we see on the macro level?

The deficit in pay tracks the deficit in productivity. Of course, the situation for public sector workers is a bit different—we actually measure their productivity mainly by inputs. If their pay goes up, their measured productivity goes up. It's hard to see how else we would do it. But the overall picture suggests that the real pay decline is down to a real productivity decline. We haven't moved away from equal pay for equal work—we've just had a big horrible recession and a sluggish recovery!