Lester was also a prominent figure in promoting birth control and abortion through the Family Planning Association, particularly in Northern Ireland.

[3] His parents divorced shortly after his birth, and he was raised by his mother, Kate Cooper-Smith, and stepfather, Harry Lester, who later formally adopted him.

[3] On 29 June 2007, Lester was appointed by Gordon Brown as a special adviser on constitutional reform to the Secretary of State for Justice.

Lester was a patron of the Family Planning Association, previously called the National Birth Control Committee.

[12][13] He sat in the Lords as a Liberal Democrat until February 2018, when an allegation of sexual misconduct was made.

[16] On 15 November 2018, by a vote of 101–78, the House of Lords referred the matter back to the Committee for Privileges and Conduct on the ground that the Commissioner for Standards had failed to act in accordance with the principles of natural justice and fairness.

[20] He said that he lacked the strength or health to continue, after the Committee disagreed with the House's conclusion regarding the fairness of the process and renewed the recommendation of his suspension until June 2022.