What happened next:

Customes officer (CO) (very formal) : "would you mind opening the rear door, sir"
Martin (M) : "You'd better stand back." (opens door. Fortunately, nothing actually falls out. Tarpaulin appears to be holding everything in - chaos behind. The bike wheels that are visible appear to lend credence to M's story of their purpose and intention.
CO and M regard interior of van.
CO and M regard each other.
CO : "I have to ask you sir, if you are carrying any firearms...?"
M : "No,"
CO : "Or explosives...?"
M: No,"
CO: "Or gas canisters?"
M: (reluctant but honest) "Well, there is a little gas canister attached to the camping stove."
CO: (almost winking) : "I expect it is a very small one?"
M: "Oh, yes, very, very small."
CO: "Well, off you go then."