A search also revealed two empty purpose-built and hydraulically operated hides.
Stewart was charged with possession with intent to supply class A drugs. He pleaded guilty to the offence at a hearing at Luton Crown Court on 23 May.
“Stewart was arrested as part of a proactive NCA investigation targeting class A drug supply. He was found in possession of a significant quantity of cocaine, with an estimated value of £4.5 million,” NCA Branch Operations Manager Adam Berry said in a statement.
“I’ve no doubt that had he not been stopped those drugs would have ended on the streets of southeast England, in the hands of gangs who bring violence and exploitation to our communities.”