The Glasgow-based firm has signed up the Post Office for the format, which is equivalent to a six-sheet poster.

More than 400 Post Office trucks have been adapted to carry the system, which will be changed every eight weeks.

"This struck us as an unusual medium with a lot of high street presence," said Post Office head of communications John Scott. "Given the amount of time our vehicles spend on the road it seemed an ideal opportunity."

Agripa's roster of printers Cestrian, Delta Display and Macro Art have shared the new work, according to sales and marketing director Roseanne Grant. She added that they have plenty of capacity to handle the firm's planned growth in the coming months of the system, which is digitally printed using ink-jet onto mesh.

Until the new format Agripa's biggest customer was Tesco, which has a fleet of 300 lorries running sites equivalent to 96-sheet posters, some of which change weekly.