The lord chancellor, Derry Irvine, has bitterly criticised the Mail on Sunday's decision to print a story about his son's drug addiction.

The newspaper questioned whether the addiction of Irvine's son was linked to the government's decision to downgrade the legal stance on cannabis.

A spokesman for the lord chancellor said: "This is a straightforward and unwarranted intrusion into his son's privacy dressed up under the spurious and transparent cover of being a story about the government's drugs policy."