Lord Sewel has quit the House of Lords and apologised for the 'pain and embarrassment' he has caused after footage emerged of him allegedly taking cocaine with two prostitutes.
The former Labour minister has bowed to intense pressure to resign from Parliament following the drugs and sex scandal, exposed in the Sun newspaper.
The married former peer said he believed he would 'damage and undermine public confidence in the House of Lords' if he stayed on.
In a statement to parliamentary officials announcing his resignation, he said: 'As a subordinate, second chamber, the House of Lords is an effective, vital but undervalued part of our political system. I hope my decision will limit and help repair the damage I have done to an institution I hold dear.
'Finally, I want to apologise for the pain and embarrassment I have caused.'
Lord Sewel, 69, faced widespread calls to step down from Parliament after the newspaper ran lurid claims about his alleged tryst with prostitutes.
The Sun newspaper today alleges that the peer boasted to prostitutes about sleeping with a BBC presenter.
He allegedly bragged: 'She was very young and it was very pleasant.'
Sewel is said to have admitted that he committed adultery with 13 women over 17 years.
It comes after he was allegedly filmed snorting cocaine off a prostitute's breast with a £5 note at his rent-protected flat in Dolphin Square, near the Houses of Parliament.
Last night the Metropolitan Police raided Lord Sewel's home with a sniffer dog and battering ram, two days after the shocking allegations first surfaced.
A group of officers, including one on a bicycle, searched the flat for three hours and left carrying several bags of evidence as part of their investigation.
The peer's departure comes just a day after he signalled he would try to cling on to his seat in the House of Lords.
He quit his £84,500-a-year role as deputy speaker of the Lords and chairman of the Lords Privileges and Conduct Committee in the wake of the scandal.
But on Monday he requested a leave of absence 'until the current investigations have been completed, when in the light of their outcome I will review my long-term position' - leaving the door open for him to return to the chamber.
Politicians welcomed his resignation.
Conservative peer Baroness Stowell, Leader of the House of Lords, said: 'I welcome Lord Sewel's decision to resign permanently.
'For the House of Lords to earn the confidence of the public, all of us must respect the privileges that come with a peerage and recognise that - because we are unelected - it is especially important to meet the standards the public have a right to expect, and to act swiftly when we fail.'
Lord Hill of Oareford, Tory former leader of the Lords, said Lord Sewel's decision to step down was 'better late than never'.
He told the BBC Radio 4 Today programme: 'I think it's the right thing to do. I think his position wasn't tenable.
'I am glad he's had a change of heart. I think if you are responsible for the setting of standards you yourself have to make sure you deliver on that.'
The scandal had fuelled criticisms the unelected House of Lords is out of touch and should be scrapped.
The chamber has swollen in size in recent years, and there are currently 783 members, making it the largest legislative assembly outside China.
And Prime Minister David Cameron is said to be set to appoint dozens of new peers to the House.
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