"Jumping on the Daily Mail bandwagon."
Actually, he's following widespread public opinion - only 9% of all voters (14% of Labour voters) think there shouldn't be a cap at all. However, 36% of voters would set the cap as low as £20 k (30% of Labour voters).
And before you sart saying "it's only the rich who want to cap benefits..." - that's wrong, too - the 9% who don't want a cap is divided equally between ABC1s and C2DEs.
Here
Mumsnet is far removed from public opinion on this issue.