The ombudsman found maladministration causing injustice by the council for agreeing to a residential development on land rented by the farmer.
The watchdog said the application violated Daventry's local plan.
However, the council said the ombudsman's decision was 'based on a misunderstanding of planning law'.
In another case, the ombudsman called on Sheffield City Council to pay£6,000 to a man with learning disabilities and his brother and carer for failing to provide services to them over four-and-a-half years. Finding maladministration causing injustice by the council, the ombudsman said there had been delays in assessing both men's needs.
In its defence, the council said that, following his assessment, the man with learning disabilities refused services.