It's my understanding that the Big Four did close a considerable number of -- pretty much, highly "marginal" -- lines (and much more often than not, to passenger only; freight continued to run) chiefly in the ten years leading up to World War II (as you intimate,
@simonw, few closures during the war years -- "almost everything was needed"). Strong impression is got, that the greater part of this branch-line closing was done by the LNER and LMS -- this contributed-to by their having been bigger, more extensive systems, with considerably greater mileage, than the other two. A fair number of lines were closed by the GWR, especially in Wales; smalle
st number of all, closed by the Southern, notwithstanding run-down by
@steamybrian as above.
Grimmest closure years in the Big Four era were 1930 and 1931. 22/9/1930 -- date of end of summer timetable -- saw the biggest single bout of closures: 17 lines w.e.f. that date; but another 27 closed on assorted dates in the course of that year (no SR lines closed in 1930; the "action" was by the other three companies). 1931 saw closure of a further 35 lines, this time by all four companies including several lines of the SR (I don't have info to hand, as to which on
@steamybrian's list these were). 1930 and '31 also saw a certain amount of closures of small "village" stations, on lines which remained in use for [semi-] fast passenger. There were an appreciable number of closures also, in other years in the overall 1929 to '39 time-span.