Back in the "good old days" there was a 0100 departure from Glasgow Queen Street for Oban. It was (I forget which) either mail or milk but had passenger accomodation as well.
In the 70s and early 80s there used to be a Cardiff - Crewe service which was essentially a mail train with a couple of Mk 1 passenger coaches attached.
In those days there were only six through trains each way on that line (plus a couple of locals Cardiff - Hereford) so the northbound from Cardiff at about 20.00, the last through train of the day, was always a sardine job.
The return left Crewe at about 1.00 am calling only at Shrewsbury, Hereford, Abergavenny, Pontypool and Newport (no station at Cwmbran in those days of course), arriving in Cardiff at about 04.20.
In those days there was also a sleeper from South Wales to Paddington (Dep Cardiff around 01.30). I think it might have started from Milford Haven and ran via Temple Meads but I can't remember it running the other way!
There was also a sleeper from the south-west to Scotland that was still running in 1992/93 as I used to see it at Bristol Parkway (around 23.15).
Until the Eurostar moved from Waterloo there were through the night connecting trains, one from South Wales and (I think) one from Crewe/Hereford. These were cut back to start from Bristol Temple Meads after a franchise change and got a lot of bad local publicity as the 2.05 from Temple Meads to Waterloo carried an average of four passengers! I think it was finally axed about three years ago.