Met Police officers stopped the vehicle in Catford on Wednesday at around 6.30pm and seized £35,000 after searching the vehicle and driver.
He was arrested on suspicion of possessing criminal property and remains in custody.
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Further searches at an address linked to him led to officers finding £4m concealed in bags across two bedrooms.
They also found 1kg of cocaine.
Commander Paul Brogden said: “This is one of the largest cash seizures we’ve seen and shows the impact that proactive local policing can have in tackling serious and organised crime.
“The arrest highlights the vital role stop and search, including stopping suspect vehicles, can play in helping officers to identify criminal activity.
“This result is testament to the persistence and dedication of the officers involved.
“We’ll continue to work relentlessly to disrupt and target those who seek to profit from illegal drugs and cause harm in our communities.”
