A spending watchdog has warned that the governemnt is pouring billions into building new free schools while existing schools crumble as they wait for repairs.

The National Audit Office (NAO) said £6.7bn was needed just to bring all existing school buildings up to a 'satisfactory' standard, with a further £7.1bn required to restore them to a 'good' condition.

But with ministers committed to creating 500 new free schools by 2020, the NAO said the Department for Education (DfE) was facing an estimated bill of £2.5bn by 2022 simply to purchase the land needed to build them.

It said the DfE has already spent £863m on land acquisitions for free schools over the last five years - in some cases paying 'premium' prices because of a shortage of suitable sites.

Richard Watts, chairman of the Local Government Association's children and young people board, said councils were 'under extreme pressure to accommodate rapidly rising numbers of pupils looking for a place'.

'No child should be without a place but councils fear that they will no longer be able to meet the rising costs for the creation of spaces, nor find the space for new classes, if they aren't given the money or powers to do so,' he said.

'If the crisis is to be dealt with properly the Government must commit to funding the creation of school places and hand powers back to councils so that they can open new schools, for both primary and secondary-age pupils.'

While free schools were helping to meet the demand for additional school places in some areas, the NAO said that because local authorities did not control their numbers they were not necessarily 'fully aligned' with their needs.

Some free schools were opening in areas where there were already plenty of places, creating 'spare capacity' which could affect the future financial sustainability of other schools in the area, it said.

The DfE has estimated that of the 113,500 new places being opened in mainstream free schools between 2015 and 2021, 57,000 would create spare capacity in other nearby schools, potentially affecting their future funding.

Official data indicated creation of spare places in 52 free schools which opened in 2015 alone would have a 'moderate or high impact' on the funding of 282 other schools.

At the same time, the NAO warned the condition of existing schools was worsening, with around 40% of the schools estate built between 1945 and 1976 coming up for replacement or major refurbishment.

As a result, the cost of restoring all schools to a satisfactory condition was expected to double over the course of the five years to 2020-21.

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