Lord Sewel is facing a police investigation after quitting as Deputy Speaker of the House of Lords over a video allegedly showing him taking drugs with prostitutes.
Lords Speaker Baroness D'Souza branded the peer's behaviour "shocking and unacceptable" and said she was calling in Scotland Yard.
"Today's revelations about the behaviour of Lord Sewel are both shocking and unacceptable. Lord Sewel has this morning resigned as Chairman of Committees," Lady D'Souza said in a statement.
"The House of Lords will continue to uphold standards in public life and will not tolerate departure from these standards.
"These serious allegations will be referred to the House of Lords Commissioner for Standards and the Metropolitan Police for investigation as a matter of urgency."