The amount found in a guest room was "minuscule, " he said, and he insisted there was no suggestion that he or any of his family were involved.

Police found less than one gram of the drug during a routine security sweep.

In a statement, the minister said:

"I can confirm that a minuscule amount of cannabis resin was found in the guest room of my home in Scotland last week. I am told that it weighed a fraction of a gram, was worth around 85p and could be years old. I have no idea where it came from, or when."

Police said such finds were common, adding: "The owner of the house is not suspected of having committed any crime".