Theresa May announced an extra £2 billion for affordable housing in her conference speech on Wednesday. Her party said that would work out at around 25,000 council homes – although that figure will vary depending on when and where houses are built.

This isn’t the first time that a government has promised a building spree. But will it join the long list of missed housing targets?

Governments since 1997 have failed to build nearly 600,000 homes. That could house everyone in Glasgow.

That’s the combined difference between total annual housebuilding targets and how many homes were actually built in each year.

Figures from the last census (in 2011) show that the average UK household contains 2.3 people.

On that basis, then, 1.3 million people could have been housed if governments had met their targets since 1997. That’s slightly more than the population of Glasgow.

We should say that this target comprises private, housing association and council houses. That means it goes beyond the scope of Theresa May’s announcement, which is about homes the government will build directly.

How did individual parties and Prime Ministers fare?

Tony Blair’s Labour government: a mixed picture

When Labour Prime Minister Tony Blair was in power (1997-2007), the national housebuilding target was 200,000 new homes a year.

For the early part of Blair’s premiership, those targets weren’t met. But in 2005, the number of homes built in the UK each year finally broke that 200,000 ceiling.

On average, across his ten years in office, housebuilding was 9,263 homes a year below target.

Gordon Brown’s Labour government: hamstrung by the recession

Mr Brown took office in 2007, just as the credit crunch began to hit.

He upped the annual target to 240,000 homes, but as the recession took hold, housebuilding dropped off a cliff. On average, the number of new homes built under Gordon Brown was 58,116 a year below target.

Cameron’s Conservative government: wary of targets as housebuilding plummets

For the first five years of his premiership, David Cameron avoided putting a figure on the exact number of homes he wanted to deliver each year.

So for the years 2010 to 2015, we’ve used the “modest” estimate from the Home Builders Federation that at the time, the target should have been 200,000 new homes a year.

On that basis, over his five full financial years in office, Mr Cameron saw housebuilding underperform by 65,128 homes a year.

In 2015, the Tories announced that they wanted a million new homes to be built by 2020-21. As such, the government is effectively committed to building around 200,000 homes a year.