The officers, members of the South East Basic Command Unit, were investigated after images of them in uniform eating together were posted online earlier this month.
The group were spotted by a member of the public in the Greenwich cafe while their patrol vehicles were parked outside.
Under current rules, cafes and restaurants are only allowed to provide a takeaway service.
The nine officers were issued fixed penalty notices of £200 following an investigation by the force.
Chief Superintendent Rob Atkin, South East BCU commander, said: “Police officers are tasked with enforcing the legislation that has been introduced to stop the spread of the virus and the public rightly expect that they will set an example through their own actions.
“It is disappointing that on this occasion, these officers have fallen short of that expectation. It is right that they will pay a financial penalty and that they will be asked to reflect on their choices.”