A large extension was built on a council officer's home in a conservation area despite planning rules which should have prevented it, according to a watchdog.
Ealing Council could be forced to pay out thousands of pounds in compensation after Local Government Ombudsman Tony Redmond criticised staff for rubberstamping the work without planning permission first being granted by councillors.
An investigation was launched after a neighbour complained about the size of the ground-floor extension and the impact it had on his home. Conservation area restrictions should have stopped it from being built, according to the Ombusdman.
He found no evidence of dodgy dealing, but said: "Nevertheless, the fact that a lawful development certificate has been issued to the partner of a council officer, who may at times have worked alongside the planning officer who dealt with the application, means the perception of impropriety is difficult to remove."
Mr Redmond suggested the council should pay compensation and more than £3,000 in legal costs to the affected neighbour, and ensure applications in which officers have an interest are reported to the planning committee.
A council spokeswoman said: "We have received the Ombudsman report and will be considering the recommendations in due course.
"We will be responding to the Ombudsman directly with our comments."