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.
More top news
Simon's Blog - In The Bleak Midwinter...
Friday night's forecast for the east of the region
Friday night's forecast for the west of the region