Cressida Dick could not solve the Met’s problems. She could barely admit they existed

There was precedent for a commissioner determined to root out misbehaviour. Failure to follow it cost her the top job

When Robert Mark was appointed commissioner of the Metropolitan police in the 1970s he wryly suggested his ambition was to ensure the service arrested more criminals than it employed.

In the five years of his leadership (1972 to 1977) Mark's success can be measured by the 50 criminal officers he put before a court, and the nearly 500 others who were swept out of the organisation as a result of his ruthless uncovering of the entrenched and institutionalised corruption which had protected them for too long.

Sandra Laville, a former Guardian crime correspondent, is now its environment correspondent