A van was stolen from New Lane in Accrington as workmen were down a manhole digging.
The "opportunist" thieves took the brand new white tipper van worth more than £16,000 at 3.25pm on Tuesday, December 14.
Police say a worker from Burnt Tree Group, a Shrewsbury business, left his high visibility jacket with the van keys inside on a bollard close to the road trench he was digging.
Sgt Simon Holderness, of Accrington Police, said: "The workers heard a screech of wheels, looked up and the van had gone.
"They have been digging on the trench and one of the workmen has gone into the trench and left his high visibility jacket on a bollard with his van keys in it. It would appear someone has grabbed the jacket and sped off."
He added: "They also stole a wacker plate worth £1,000 and a pile extractor valued at £500. It's an opportunist theft. The van hasn't been recovered but some items have. Paperwork and magnetic strips were found discarded on Whitecroft Lane at the top of New Lane."
Anyone with information regarding this incident can contact Sgt Simon Holderness on 01254 353775.