Both the government and Conservatives are promising more school places - but official figures show there is already a surplus of more than 700,000.
There are falling numbers of primary-age children
In this week's party conference, the Tories made the creation of 600,000 more places a centre-piece of plans to increase school choice.
They argue that by expanding school places, parents will be able to have a wider range of options.
But in some local authorities, a fifth of school places are already "surplus".
The availability of surplus places in England's schools has become a hot political issue - as both parties promise to increase parental choice.
Conservative education spokesman, Tim Collins, promised to "make choice a reality" by funding 600,000 extra places - and removing "the rules which stop good schools from expanding or new schools from starting".
482,000 surplus primary school places (11%)
231,000 surplus secondary school places (7%)
Total school places capacity: 7.9m
Camden, Solihul only 1% spare places in secondary schools
Knowsley 20% spare primary places
The Education Secretary, Charles Clarke, has said in response that "hundreds of thousands of extra places" are already being created.
But the figures on surplus places, published in a written ministerial statement earlier this year, show the excess capacity already in the system - in part driven by the falling number of primary-age children.
And it highlights that it is not numbers of places - but where they are available - that will be of interest to parents.
The figures, for January 2003, show that in primary schools there were 482,000 surplus places (11% of the total capacity) and in secondary schools, there were 231,000 surplus places (7% of the total capacity).
'Extra' or 'new' places?
The figures understate the full picture to an extent because only schools with more than 30 surplus places were counted.
This also puts in perspective the scale of the increase needed to expand choice - with the total number of places approaching eight million.
Asked where the "extra" places were being created, Mr Clarke's officials mentioned 20 new schools in London, the ability of schools to open new sixth forms, and the plans for 200 city academies around England.
City academies usually replace existing failing schools - but an aide of Mr Clarke's said these often had low pupil numbers, so in practice "new" places were being created.
The latest official data on spare places showed very wide variations among different education authorities, ranging from 9,832 in Hertfordshire (11% of the local total) to 84 (1%) in Camden, London.
In terms of percentages, Hammersmith and Fulham in London had an 18% surplus in secondary places, while Knowsley had a 20% surplus in primary places.
In contrast, the London Borough of Enfield had only a 4% surplus in primary places, and Bolton, Bromley, Bury, Camden, North Somerset, Poole, St Helens, Sheffield, Solihull and Torbay had only 2% or less spare places among secondary schools.
This also highlights the dispute over the so-called "surplus places rule".
This is the notion that popular schools are not allowed to expand if there is spare
capacity in other schools locally - which parents say forces their children into schools they do not want.
The Conservatives once again promised to abolish this restriction this week. But the government says
no such rule exists.
Education Minister Stephen Twigg has said that schools are already able to expand.
"We have provided the opportunity for the most successful schools to expand where such potential exists".
But when pressed on which schools had done so, Mr Miliband named just
four: two in Bury, one in Bristol and one in Wokingham.