Mistaking a police car for a taxi is embarrassing, doing so while carrying a vast quantity of pot is a catastrophic error.

It has left a drug dealer in Copenhagen facing the threat of a jail term, the Local reported.

According to Copenhagen Police's Twitter feed, the man was carrying around 1,000 joints when he clambered into the patrol car.

"Last night a cannabis dealer from Christiania who wanted to get home quickly got into a taxi. He received a big surprise when he realised it was actually a police car he was sitting in," police wrote.

"The police officers were happy to see him since he was carrying around 1,000 joints," the tweet continued.