The council’s current drugs and alcohol policy was adopted in May last year.

Substance testing was deemed unnecessary in an amendment introduced by the Greens and supported by Labor, SNP and Liberal Democrat councillors.

But the council’s Conservative group leader, Iain Whyte, said any accident caused by a driver under the influence of a HGV would be “catastrophic”.

He said: “The audit shows that this policy needs to be changed as soon as possible.

“People running council business should be checked to make sure they are safe, not only for their own benefit but also to protect the community.”