Media playback is unsupported on your device Media caption The prime minister said it was up to parents to "make sure your children attend school" and avoid sanctions.

Parents in England who refuse to pay a penalty after their children play truant will have their child benefit docked, the prime minister has said.

A civil penalty of up to £120 would be claimed through child benefit if the fine is not paid after 28 days. Currently, just over half of fines are paid in that period.

David Cameron told BBC Breakfast it was about making sure children get "the great start in life that they need".

Teaching unions said docking child benefit could end up hurting children.

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The existing system sees non-payment of the £60 civil penalty in England being doubled to £120 after 21 days, and subject to prosecution after 28 days. But many parents do not end up in court because councils do not take legal action.

David Cameron said the system must be changed because truancy was harmful to children's life chances.

"All the evidence is that if children consistently miss school, they get a worse education, they get worse results and as a result they have less good prospects for the rest of their lives," he told BBC Breakfast.

"So this is about making sure our children get the great future and the great start in life that they need."

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At the Conservative Party conference in Manchester, he is expected to say: "There is nothing responsible about allowing your child to go without an education.

"So for parents who let their child play truant and refuse to pay truancy penalties, we will deduct it from their child benefit."

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The Press Association says it obtained figures earlier this year which showed 16,430 people in England were prosecuted last year for failing to ensure that a child went to school.

About three-quarters - 12,479 - of these were found guilty, and courts issued 9,214 parents with fines worth an average of £172.

Mr Cameron first spoke of the idea of cutting benefits for parents of regular truants in September 2011.

And a key government adviser on school behaviour called for the same measure in April 2012.

But Chris Keates, general secretary of the teachers union NASUWT, said docking benefits was not the answer.

"For some families all that this will do, of course, is increase the chaos and it will increase the deprivation," she said.

"It won't actually solve the problem and in the middle of all of this is a child who's not getting their entitlement to education..."

Meanwhile, the prime minister will also announce a new right for parents in England to request that schools provide breakfast and after-school clubs or holiday care.

Schools will not be obliged to provide these when asked, but will have to publish reasons why they do not respond to such requests from parents or childcare providers.

This will apply to all state-maintained primary schools, as well as new academies and free schools.

Update 8 October 2015: We have amended a figure in this report to clarify the number of fines that are paid within 28 days.