Donald, 37, a detective constable, was yesterday jailed for 11 years for corruption at the Old Bailey and Cressey, 38, received seven years' in prison.
The conviction of both men has sent shock waves through the police service and raised worrying questions about a system in which officers are able to obtain confidential information for their own use and manipulate the criminal justice system with apparent impunity.
Since the case involving the Metropolitan Police only came to light because of an investigation by BBC TV's Panorama, there are concerns that more corrupt officers may be operating undetected.
Donald's conviction has resulted in significant changes to the management structure of the South East Regional Crime Squad (Sercs), provoked a review of informer handling, the investigation of at least eight other officers and the collapse of six cases in which he was involved.
In addition, an international investigation into the activities of two suspects, including Kenneth Noye, who is being sought by police for questioning about the M25 road rage killing, has been aborted, and the national telephone tapping unit may have been compromised.
The Donald case stemmed from a raid on a flat in Streatham, south London on 1 September 1992. Cressey and David Fraser were arrested on drugs offences, which the men deny.
Fraser was given bail and immediately fled to Spain. His extradition is being sought.
Cressey told police he could supply them with information in exchange for his own freedom. He agreed to become an informer and was, surprisingly, given bail. It later emerged this was due to Donald's intervention, for which he received an pounds 18,000 bribe from Cressey.
Donald was assigned to work with Cressey as his police handler, but instead of obtaining information he soon started accepting more pay-offs, including pounds 1,000 for a copy of Cressey's police file and an agreement worth pounds 40,000 to remove and destroy an incriminating surveillance log.
For pounds 1,000 Donald also agreed to hand on information, via Cressey, to Kenneth Noye, who served eight years for his involvement in the Brink's- Mat robbery, and Michael Lawson, a London car dealer, about an international police drugs operation.
Cressey also paid pounds 500 for sensitive information about surveillance on Mr Lawson. Donald was able to obtain legitimately the confidential information from another Metropolitan Police officer working at the National Criminal Intelligence Service.
It later emerged that Donald was also in possession of confidential information, including details of telephone taps and other material which may have compromised investigations by both the NCIS and other police forces.
At the beginning of March 1993, Donald and Cressey's relationship soured. Cressey was charged with a serious offence and he decided to expose his corrupt new friend in the hope of saving himself.
On 22 March he contacted the BBC's Panorama team and for the next six months they secretly recorded 14 meetings and conversations with Donald.
The BBC programme "The Case of India One" was broadcast on 27 September 1993. It showed Cressey and Donald meeting in a car park and money passing between them in a carrier bag.
The police only got wind of the investigation days before it appeared on television after they were tipped off by FBI agents. Following the programme, two officers, one from NCIS and another from Sercs, were arrested and questioned by Scotland Yard's Complaints Investigation Bureau, but no evidence was found against them.Both are suspended from duty on unrelated matters.
Donald was charged with perverting the course of justice and, in November 1995 during his Old Bailey trial, he admitted to four charges of corruption. Throughout both Donald and Cressey's trials the jury were placed under 24-hour police protection.
After the case yesterday Commander Roy Clark, regional co-ordinator of Sercs, said: "Donald was more than corrupt, he committed acts of treachery beyond belief. He sold operational secrets to those involved in organised crime that put the lives of police officers at risk.
"By doing this he became part of the criminal underworld which the public had paid him to combat. The damage he has done to the efforts of policing and in particular to the efforts of Sercs has been considerable."Reuse content