Police are appealing for witnesses after an off-duty officer was stabbed when he tried to stop a robbery in south London.

The 37-year-old saw four men on mopeds trying to steal another moped shortly before 6pm on Saturday.

According to Scotland Yard, the suspects were armed with a large kitchen knife.

The officer, who has not been named, challenged the group, who were targeting a 21-year-old in Lewisham.

He was stabbed in the leg, but refused to back down and the moped gang eventually fled empty handed.

The 21-year-old victim was left with bruises but his injuries are not life threatening.

Lewisham Police are trying to identify those responsible.

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A spokesperson said: “Officers are keen to hear from anyone who either witnessed the incident or has information that could assist the investigation.”

:: Anyone with information is asked to call Lewisham Police on 101, quoting reference CAD5786/11AUG, or call Crimestoppers, anonymously, on 0800 555 111. Alternatively, witnesses can tweet @MetCC.