A public service announcement -
National Rail Enquiries is showing some trains in to late evening on Xmas Eve that will not be running (looked something up for someone else and saw it was all balls.)
Broadly, the national rail network shuts down by about 10 pm on Xmas Eve - as in the trains are back in their boxes and train crew on their way home round 10 pm, not last departures round 10 pm, so the longer the journey, the earlier the last departures, if you see what i mean.
Also some train operators are reporting cancellations because of train crew off sick / self isolating.
This is TFL's page for xmas eve - broadly most of their services running until about 2300 - midnight, but no night buses / 24 hour routes in to Xmas Day, and some bits of overground pack it in round the same time as national rail.
Buses outside London tend to do their own thing, so check with the local operator/s, but it's fairly common (assuming there are buses of an evening) to pack it in round 8 pm, or run a much reduced service late evening.
And in many cases it may be amended / Saturday timetable to start with.