The UK Health Security Agency has issued a yellow cold health alert for south-west England, effective from 6pm on Christmas Day until 12pm on 27 December.
The alert warns of minor impacts on health and social care services, including increased healthcare use and a greater risk to vulnerable people due to low temperatures.
Met Office spokesperson Oli Claydon said that a white Christmas is "highly unlikely," with "pretty decent" and mainly dry conditions expected across the UK, though cooler temperatures and strong easterly winds are forecast.
Christmas Day temperatures are predicted to reach around 7C in north-east England and 6C in the south, with overnight frost and freezing temperatures, potentially dropping to minus 6C in rural Scotland.
The RAC anticipates Christmas Eve will be the busiest day for car travel, with 4.2 million trips expected and heavy traffic on major roads like the M25 and M5 between 1pm and 7pm.