Maddy Prior and the Carnival Band produced a number of albums back in the 80s: some great stuff on them: Carols and Capers, Gold, Frankincense and Myrrh, and A Tapestry of Carols. There has been a more recent compilation double CD -and live concerts - featuring the best of these. Well worth investigating.
Also Barbara Dickson has a really lovely CD, simply called "Winter" - a mix of carols, solstice and other secular songs on that theme.