Shades of Paul Verhoeven in this story
https://www.google.co.uk/imgres?imgurl=http%3A%2F%2Fi.ytimg.com%2Fvi%2FY6v_nrf9nFQ%2Fhqdefault.jpg
The weight of the Hummer limo, and its 8mpg compared to the weight and mpg of a double-decker bus or a coach would be relevant to the story. I sometimes feel cheated by newspaper articles which skimp on precisely the facts that spring to mind when astronomical costs are bandied about, like this.
Serco must have lost a packet on the trip. Why not furnish them with coach tickets?
Were their thought that they'd abscond if allowed to travel under their own initiative?
Was it that they weren't permitted any cash or means of independent travel choices?
Were they, in any sense, being 'escorted' up north by Serco, a prisoner transport contractor?
@aog
You should be able to select retrocop's later best answer, should you wish.