Heritage Railways hold over 1000 special events every year. Events for all the railways for the next few months are listed here.
Nearly all railways hold Santa Events on every weekend in December, so I don't list those here as it would just fill the Diary and make it hard to find any other event types during the Christmas period.
Events for 2018 will be added over the next few of months (It takes a long while to complete as some railways do not list their events until well into the new year).
For a full listing of events for any particular railway, please visit that railway's own website.