A quick look at the current shortages:
A 15:27 London Paddington to Oxford due 17:17
C 15:40 Bedwyn to London Paddington due 16:57
B 16:37 Oxford to London Paddington due 18:31
A 17:37 Oxford to London Paddington due 19:31
C 17:44 London Paddington to Reading due 18:44
B 18:42 London Paddington to Bourne End due 19:29
C 18:48 Reading to London Paddington due 19:46
B 19:34 Bourne End to Maidenhead due 19:45
B 19:49 Maidenhead to Bourne End due 20:00
C 19:50 London Paddington to Banbury due 21:23
A 19:57 London Paddington to Oxford due 21:44
B 20:05 Bourne End to Maidenhead due 20:16
C 21:38 Banbury to London Paddington due 23:24
C 23:49 London Paddington to Reading due 00:56
Services "A", "B" and "C" could run into each other (I may not be 100% there with my guesses) and that looks like a total of perhaps 4 or 5 carriages less operating that is required from a fleet of 152. Yes, that's 3.3% of the fleet out when it should be in, and I suspect uncomfortable on the 17:44 and more so on the 18:42 out of Paddington (5 rather than 6, and 4 rather than 2 carriages). I count 51 departures in the 2 hours from 17:00 to 18:59, none cancelled and 2 short formed. So about 2% capacity down. 2% more than it should be (and all in one train group) - but worth quoting what is running at full strength as wells what isn't to see it in perspective.
Looking at current train running there are already 14 short formations listed between now and midnight on the Thames Valley lines...........all down to "train faults" - judging by the comments of those in the know this is as much down to planned servicing/refits so why not say so?
.....or are we really looking at this situation for the foreseeable future as the remaining units are being flogged to death and are reaching the end of their useful/reliable life, with nothing in reserve?
Gawd I hope not is we're to get those as hand-me-downs in the Bristol area!