On 12 May, 20:25, Basil Jet wrote:

I assumed he meant "are these the first diesel trains utilized for
passenger service *acquired* (as opposed to inherited) by TfL and its
predecessors?" In which case the answer AFAIK is yes. LUL does own a
diesel loco or two for maintenance purposes.

The answer is no, if you include experimental use on booked services.
London Transport tried out an AEC diesel railcar for some months on
the Chesham branch and also Epping-Ongar c.1954. This was before
either line had been electrified, and presumably LT was wondering
whether it was worth doing. As we now know, Chesham was eventually
electrified 1960/1961. Epping-Ongar was also given third and fourth
rails c.1957 but of course has since been closed.