He was speaking after launching the policy paper on the environment and a sustainable economy and society, which tackles the population 'explosion'.
The document, to be debated at next week's conference, advocates 'adequate, safe, confidential family planning advice' for everyone from puberty onwards, and sex education appropriate to the age of the child as part of UK schools' core curriculum.
The remarks brought condemnation from Conservatives but a Liberal Democrat spokeswoman said later: 'The key is confidentiality so that a child as young as 11 can receive adequate advice. It does not mean that doctors or clinics will automatically prescribe.'
She added: 'It is gross hypocrisy for the Tories to criticise single mothers on the one hand but condemn them to ignorance on the other.'