Carol Services are a common question on here-
Two which are slightly out of the ordinary are-
York Minster- Sankta (St) Lucia Festival of Light-
St Lucia Day is a big festival in Scandinavia (13 December) marking the longest night of the year in the Julian Calendar. York, of course, has strong Nordic/Viking/Scandinavian (whatever word you choose) links, and a thriving Scandinavian Society.
So this service has been happening since 2013.
It would be well worth a day trip from London, ending with this service. I have just been watching a recording of this year's service (held last night, 15 December).
and
Leigh on Sea St Clement's Church Folk Carol Service
This is always on Gaudete Sunday (mid Lent, 14 December this year). St Clement's was my Parish Church for 10 years while living there (I rarely actually got there due to working 7 day weeks in London), and is an easy trip from London Fenchurch Street on the C2C line. It is a very different but very interesting service, Carols before the Victorian style which we are all familiar with now.
Part of my annual Calendar, now that it is live streamed.