BoCo was to show the visiting diesel around, but when he saw steam engines in the shed he refused to go further and insulted the railway for keeping them in service. A furious James bestowed upon him the nickname "Old Stuck-Up".
The next day, Old Stuck-Up was about to leave when he remembered he needed refuelling. He attempted to use BoCo and Bear's part of the shed to be refuelled and cleaned, but slid on cleaning fluid on the rails and crashed into the back of the shed. He was sent home after being talked to severely by the Fat Controller; BoCo noted that while he couldn't hear everything, he didn't think it sounded particularly flattering.
Old Stuck-Up is rude and arrogant like a lot of diesels, and believes that steam power is subpar to diesel.
Old Stuck-Up is based on a BR Class 40 1Co-Co1. The Diesel is another member of this class. Unlike most diesels in the Railway Series, Old Stuck-Up's number wasn't fictional. The real 40 125 was built in December 1960 as D325 and was the first member of the class built with "split" headcode boxes. It was withdrawn from service in May 1981 and cut up at Swindon Works in December 1983. Seven Class 40s are preserved, the first built, D200, at the National Railway Museum.
Old Stuck-Up is painted in the British Rail "Rail Blue" livery with yellow warning panels. The number "40 125" is painted on the sides of his cab in white.
- Due to the real 40125 being scrapped in 1983, the setting of "Old Stuck-Up" likely took place before that date.
- Old Stuck-Up bears a heavy resemblance to D199.