The 22-year-old man from Lambeth was stopped by armed officers on Edge Lane in Liverpool at around 8.45pm on Saturday 6 March and found in possession of a handgun.
The arrest was a joint operation lead by the Met’s Specialist Crime Command in partnership with colleagues from Merseyside Police.
Detective Inspector Seton, from the Met’s Specialist Crime Command, said: “This cross border operation shows that we will relentlessly pursue violent criminals across the country in order to prevent guns from reaching the streets of London.”
The man is currently being questioned by detectives at a south London police station. Enquiries continue