This short video, from one "goonerlewis16", shows the traditional Pullman carriages being hauled through Strood here in Medway, by a Class 67 diesel-electric locomotive at each end – 67 024 at the front, and 67 019 as the so-called banking loco to help push the train up steep inclines. Presumably there must have been at least one such elsewhere on its journey.
Visually, the cyclopean Class 67 isn't a very attractive loco, but it does the job well enough, with the power of a top-end Type 4 diesel, though not as high as a Type 5 (e.g. Deltic) but with a higher top speed.
If it's just extra hauling power that's needed, both locomotives will be joined together at the front, but for climbing long and/or steep inclines, the second loco goes at the back. After all, we all know how much easier it is to push (say) a heavy trolley of shopping or suitcase-on-wheels up a slope from behind than it is to pull on it from in front.
This train has the good fortune to have both...