NRE’s journey planner appears to erroneously add an extra hour to the journey time if the journey crosses 01:00 on the day that daylight savings time ends. An example is the 23:09 departure in this screenshot which NRE thinks takes 3 hours. Other planners such as FastJP.co.uk correctly identify this itinerary as taking 2 hours.
Yes I believe @maniacmartin has spotted that factor but the issue is that unlike other journey planners NRE hasn't!
Looking at 9T21 2335 Bedford - Brighton 0228 which is running at the changeover time. NRE shows dep 2335, arr 0228, duration 3:53, which implies the train will stop at 0200 BST, wait for an hour until 0200 GMT, then carry on to Brighton. FastJP shows dep 2335, arr 0228, duration 2:53, which isn't really correct as either it arrives at 0228 GMT, or it has a duration of 2:53, it can't do both. I think the issue is the data doesn't specify whether a particular time between 0100 and 0159 is BST or GMT, so websites have to guess. In practice I suspect the train will run to BST throughout.
If the data doesn't specify BST/GMT, is there a documented convention that the offset doesn't change for timings within a single train record? Even so, timings for trains that start between 0100BST and 0159GMT would be ambiguous.
"Daylight saving time"? Never heard of that [after all, it doesn't save any daylight, so it would be an illogical name for it] - surely it's called "summer time"...
The particular time zone that the UK uses for the summer months is known as 'British Summer Time'. However we aren't the only country in the World that puts the clock forward for summer, and 'daylight savings time' is the generally accepted international term for the practice of having a time zone one hour further forward in the summer months. In other words, both terms are correct, but 'British summer time' refers specifically to the UK, whereas 'daylight saving time' could refer to any country.
As I recall and I will check later in one of my vintage volumes, in the printed BR timetables there was a timetable note “1 hour earlier” (or later ) on the specific dates when the clicks changed A neat advantage Of clarity over the IT !