A MET officer had to go to hospital after an incident in Acton on Saturday evening.
Police were called to two men behaving suspiciously near bins in Clandon Close at around 9pm.
The men were thought to be storing or accessing weapons.
One became aggressive and a male constable suffered a broken finger as he detained the suspect.
Both men were arrested and taken into custody, one on suspicion of assault and the other for possessing an offensive weapon, a crowbar.
The officer has been discharged from hospital, but his hand injury will require ongoing treatment.
Supt John Tibaldi said: “Tackling violent crime is the Met’s top priority, and that includes dealing robustly with those who assault our officers and other emergency workers.”
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