Mark's paramount concern was that Scotland Yard should maintain its autonomy, and that the police themselves should handle complaints against the force – or service, as it was by then becoming known. Although far from dyed-in-the-wool "old school", Mark believed in police inviolability, arguing that freeing them from political or bureaucratic interference was essential to the preservation of democracy.
"The police must not even seem, in dealing with industrial disputes or political demonstrations, to reflect the wishes of the government of the day," he wrote in his memoirs, published in 1978. "Their manifest impartiality is their most priceless asset."
Mark's views on the handling of complaints against the police were at odds with those of Roy Jenkins, the Home Secretary who had first appointed him. Faced with growing evidence of police misconduct, Jenkins insisted that complaints should be investigated by an independent body, enjoying public confidence.
Mark indignantly insisted that what was proposed would undermine police discipline and compromise effective investigation. When the bill was enacted, Mark resigned rather than administer legislation that he could not accept.
Robert Mark was born on March 13 1917 in the Manchester suburb of Chorlton-cum-Hardy, the youngest of five children. His father prospered in the clothing trade, but when the family moved to a bigger house, Robert saved his bus money by walking to and from William Hulme's Grammar School. Although undistinguished academically, he became captain of rugby and head prefect.
His first job as a carpet salesman bored him, and in 1937 he applied to join the Manchester city police, to the dismay of his father who protested that it was only one step better than going to prison. Released for military duties in 1942, he trained at Sandhurst and was posted to 108 Tank Brigade. He then transferred, thanks to the influence of his elder brother James at the War Office, to a more exciting role with the Phantom (GHQ Liaison) Regiment, which liaised with specialised commando teams. At the end of the war Mark found himself, as an ex-policeman, promoted to staff captain and posted to the military government in Germany, where he remained until his demobilisation in 1947 in the rank of major.
Back in Manchester, working in Special Branch as a detective sergeant, Mark toyed with leaving the police. But a series of rapid promotions landed him in the chief constable's office as chief superintendent in charge of administration, younger than the youngest inspector in the force.
When Mark's application for the assistant chief constable's job at Newcastle-upon-Tyne was rejected, he enrolled for a course at the Police College, the only one he attended in his 40-year police career. "I must be the classic example," he recalled, "of the man who beat the system."
On New Year's Day 1957, Mark took over as chief constable of Leicester. Dropped off in his new Ford Consul by his brother (Mark had yet to learn to drive), he was startled to discover that under the genial rule of his predecessor, staff at police headquarters went home for lunch. Abolition of such domestic excesses was followed by more visible reforms; in 1961, to general acclaim, Mark cancelled an order for hundreds of parking meters and instead established a corps of traffic wardens administering a fixed penalty system.
Following the escape of the Soviet spy George Blake from Wormwood Scrubs in 1966, Mark served on Lord Mountbatten's inquiry into prison security. It was on his return from a visit to Dartmoor amid the clamour caused by another escape – that of Frank "Mad Axeman" Mitchell – that Jenkins offered Mark the post of assistant commissioner at the Met. Mark was appointed deputy to Sir John Waldron the following year, and Commissioner in 1972.
In November 1969 The Times had exposed corruption in the Met's CID of such an astonishing scale that one leading criminal lawyer likened it to catching the Archbishop of Canterbury in bed with a prostitute. Mark said the story "rocked the Metropolitan Police to its foundations".
The implications were still reverberating when, in February 1972, the Sunday Mirror disclosed that the Flying Squad's commander, Kenneth Drury, had been on holiday in Cyprus with a Soho businessman and celebrated villain called Jimmy Humphreys. Drury, suspended and forced to resign, was eventually jailed for eight years for corruption. Within a matter of weeks, Mark, with his provincial pedigree and reputation as "Mr Clean", took charge of the biggest and most complex police force in Britain.
Mark's famous observation that "a good police force is one that catches more crooks than it employs" was matched by drastic action. He set up A10, a criminal investigation branch within the Yard. Mark had discovered that the existing anti-corruption squad was headed by a policeman who was himself corrupt. Det Ch Supt Bill Moody, doubling as head of the obscene publications squad, had been extracting protection money from Soho pornographers; he was jailed for four years.
Mark's efforts, at a moment of deep shame for the Met, encouraged the honest majority within the force, and resulted in the resignations of several hundred detectives. But Operation Countryman, one of the biggest and longest investigations ever into police corruption, failed to stop the rot; and Mark's premature departure in 1977 was followed by a series of scandals that suggested to the public that half the detectives in London were on the take.
Mark's reign as Commissioner coincided with heightened terrorist activity in the capital, particularly from the Provisional IRA. In 1975 alone 10 people were killed and 169 injured in a total of 29 bombings and other incidents. These included the Balcombe Street siege, in which a gang of IRA gunmen – "four seedy, cowardly degenerates", as Mark later described them – took a couple hostage at their flat in Marylebone. Mark took personal command and put the SAS on standby. Hearing this on the radio, the gang surrendered; the hostages were unharmed.
In the same year Mark negotiated a successful conclusion to the Spaghetti House restaurant siege in Knightsbridge, the case he recalled as the most difficult of his career. Having bungled the theft of the restaurant takings, a gang of gunmen had taken nine Italians hostage in a smelly, cramped basement. With the police ensuring that the gunmen received only bad news, such as the suggestion that one among them was selling information to newspapers, the hostage-takers surrendered as the siege entered its sixth day, without a shot being fired. Among those to congratulate Mark was Lord Mountbatten.
Mark's most surprising appearance as Commissioner was in a series of television commercials for car tyres that ran from 1974. His wooden endorsement ("I believe Goodyear tyres make a major contribution to road safety") ensured cult status for the campaign.
In retirement he held several directorships and wrote his memoirs, In the Office of Constable. He was awarded the Queen's Police Medal in 1965 and knighted in 1973.
Robert Mark married, in 1941, Kathleen Mary Leahy, who died in 1997. Their son and daughter survive him.
