Constable Michael Butler, 47, who has been commended three times for bravery during a 30-year career, admitted two charges of corruptly accepting the money in return for destroying the file.
Nicholas Browne, for the prosecution, told Oxford Crown Court that Butler, of Kidlington, Oxfordshire, was given the money by his friend Trevor Gladwell, of Oxford.
Mr Gladwell had been arrested for a drink-driving offence but he wanted to keep his driving licence because he ran a parcel delivery service.
Initially, Butler told his friend to see a solicitor but Gladwell started negotiating over the telephone with the policeman about solutions to his problem.
The two men shared an interest in Carterton Football Club in west Oxfordshire and drank together at the Pennyfarthing public house in Oxford. There were subsequent meetings in the pub and in Gladwell's office as the prosecution file was being prepared, said Mr Browne.
Butler revealed to his friend that he had seen the prosecution file and had taken it.
'It was agreed the sum of pounds 4,000 would be paid by Gladwell to the defendant for the complete file to be destroyed.' Butler burnt the file in his back garden after the first instalment of pounds 2,000 was paid.
With no evidence to prosecute Gladwell, the Crown Prosecution Service had to discontinue the case. However, Gladwell did not pay the second instalment. Days passed without the second instalment appearing and Gladwell consulted another solicitor near Bristol, and Avon and Somerset police were alerted.
Gladwell agreed to co-operate with them after being granted immunity from prosecution. 'It was considered more important to prosecute a corrupt police officer than a guilty motorist,' said Mr Browne. Police gave him the second instalment and secretly kept watch as he handed the money to Butler.
Mr Browne said Butler had confided to a detective during a golf match in Oxford that he was facing an expensive year. His remarriage was going to cost pounds 3,000, followed by a pounds 6,000 honeymoon in California.
Philip Shears, for the defence, said Butler would never have appeared in court but for spotting his friend's file on top of a pile of documents at the Thames Valley Police headquarters in Kidlington, where he worked in the administration support unit.
'Gladwell was in a real panic, indicating he would do anything to get out of the situation he was in,' he said.
Jailing Butler for 18 months, Judge Richard May told him: 'You not only let your police colleagues down. It is essential that public trust in the police exists and you corruptly abused that trust.'Reuse content