The PM said the he had no plans to legislate, although he hinted ministers would not stand in the way of MPs attempting to introduce a backbench Bill.
Meanwhile, Home Secretary Theresa May echoed Culture Secretary Maria Miller earlier this week in suggesting a more limited reduction to 20 weeks.
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Wednesday's afternoon forecast for west of the region
Wednesday's afternoon forecast for east of the region
The report highlights 17 schools that failed to achieve 'Good' Ofsted inspection results in over a decade.