Which EU/UK train companies provide plug sockets, which are free, and on which services? [closed]

UK answer.

Fast long distance "intercity" trains and some newer "regional" trains tend to have sockets in the seating areas for the passengers to use, these are usually these are often labeled something like "laptops and mobile phones only" reflecting their intended use. Local and "regional" trains are less likely to have them. There is no charge for using them. The sockets are standard BS1363 ("type G") sockets. Note that the sockets frequently have metal face-plates. Some dodgy travel adapters have been known to cause short circuits when used with metal faced sockets.

Socket locations and quantity vary between train operators and models but as a general rule seats with tables are more likely to have them than those without and seats in first class are more likely to have them than those in standard class. Usually there is one socket for a pair of seats but some older coaches (not sure if any of these are still in service) had one socket per table (a table normally has four seats).

You also get sockets that are not intended for public use and are labeled as such. Often in the back of luggage racks and similar locations. Sometimes people use them anyway and sometimes this gets them into trouble (though from what I can gather most of the time they get away with it). Some of these sockets also have warnings that voltage and frequency may vary......

Some of the most recently refurbished trains have USB charging in addition to the "type G" sockets. It also seems that at least some "EMR regional" trains have USB charging points but not mains sockets.