Can confirm.
You know, on the first album it probably is something like a Bassman. I've never heard anything very definitive other than the rented Jazz bass thing, but nothing regarding amps for the first album, so it was probably whatever the studio had. The bass tracks definitely don't sound as raunchy as the Beck-Ola pieces. Even then, who knows what they actually used in studio for those tracks, but comparing that sound to other recordings of Marshalls+rotos, I'd wager it is the Tele into a Mic'd Major. On some of their American dates I know the entire band used Plush Amps as well, which iirc were based of a Fender Showman circuit (Fender something anyways).
Here you can see the sizably larger Majors towering over both the band and the other Marshalls (looks like the Grande in Detroit):
You can also see them here, however with another bass player (Ronnie isn't there, but Mickey Most is, so it's pre-Beck-Ola):
Whoever that chap is though, he shows up again here, in the rear, while Ronnie plays guitar along with Jeff:
And here is the Plush backline:
Sorry for the side track.