More than 23,000 police officers and staff are moonlighting in second jobs, with the figure soaring nearly 20% in a year, the Mail on Sunday reports.
The figures mean more than one in 10 officers in England and Wales earn a second income from non-police work, according to an investigation by the paper.
At the same time, the number of investigations into potential rule breaches has tripled, raising questions over conflicts of interest arising from second jobs.
Some officers may work in self-defence training, for example, therefore meaning police forces may be commissioning off-duty staff to carry out such work for them, the report claimed.
A total of 23 of England and Wales's 44 forces did not check to see if they were paying companies run by their own officers for work.