The former top counter-terrorism officer at Scotland Yard resigned as the UN’s chief of security yesterday after an inquiry faulted his department for the worst terrorist attack on UN staff.

Sir David Veness, who co-ordinated Britain’s anti-terrorism efforts as the Metropolitan Police’s Assistant Commissioner for Special Operations, said that he “was willing to shoulder full responsibility for any security lapses” that preceded the suicide bombing of the UN office in Algiers on December 11 last year .

The departure of the veteran detective casts a shadow over sweeping reform of the UN security structure after a bombing of the UN office in Baghdad on August 19, 2003, which led to Sir David’s appointment to head a new Department of Safety and Security (DSS).

The Algiers attack killed 17 UN staff – a higher UN death toll than the Baghdad bombing, in which 15 of the organisation’s staff were among the 22 dead.

Sir David’s resignation coincided with the publication yesterday of an inquiry into the UN security system led by Lakhdar Brahimi , a UN trouble-shooter and former Algerian Foreign Minister. Mr Brahimi’s panel found that that the Algiers bombing came after numerous internal UN warnings about a terrorist attack by the al-Qaeda affiliate in the Maghreb.

A security risk assessment sent to the responsible UN security official in Algiers in October last year rated the risk of terrorist attacks, including vehicle-borne suicide bombs, as critical and very likely, with a predicted critical impact, the inquiry said.

The panel said that the UN, under pressure from the Algerian Government, failed to raise the threat level from the minimum of 1 on a 1-5 scale despite other large-scale bombings in Algiers. The UN asked the Algerian Government to install bollards in front of the UN building and make the street one way. The UN considered moving premises when the Government failed to do so, but did not identify a suitable new office.

The Brahimi inquiry called the DSS’s response to security warnings inadequate and said that the UN must improve “accountability, leadership, and internal management and oversight”.

Sir David was named to lead the revamped UN security structure in 2005 after being in charge of Britain’s fight against al-Qaeda at the Metropolitan Police. He was a member of the negotiating team during the siege at the Iranian Embassy in London in 1980 and led efforts to end the stand-off at the Libyan Embassy after the shooting of a police officer in 1984.

At Scotland Yard he ran the anti-terrorist squad, Special Branch and royal and diplomatic protection teams. He played an important part in the Met’s decision to call in the Army with personnel carriers to Heathrow. But he had to apologise to the Royal Family after the “comedy terrorist” Aaron Barschak gatecrashed Prince William’s 21st birthday party at Windsor Castle.

At the inquest of Diana, Princess of Wales, he denied that he sat on a legal document suggesting that the Princess feared a plot to kill her in a car crash.

Sir David was in Jordan on his way to Baghdad when the Algiers bomb exploded and went to the scene immediately. He conducted his own internal inquiry, acknowledging the need for a fuller investigation.

Ban Ki Moon, the Secretary-General, had come under pressure from UN staff unions to set up the independent inquiry after claims that Babacar Ndiaye, the Senegalese UN security officer in Algiers, who died in the attack, had tried to raise the alarm. His widow, Selbe, complained that the UN ignored her husband’s pleas for greater protection against a terrorist attack.

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