The lowest temperature in the UK at the weekend was recorded in Buckinghamshire.
A temperature of -19.6C was recorded at Chesham between Saturday night and Sunday morning, the Met Office said.
During the weekend heavy snow fell in Hertfordshire, Buckinghamshire and Bedfordshire.
Chiltern Railways is operating a reduced service, with two trains per hour to most stations.
Luton Airport reopened over the weekend but passengers were warned to face delays.
Drivers have been urged not to travel unless necessary.
Some residents in Buckinghamshire said the temperature felt colder between Sunday and Monday but the lowest recorded temperature overnight was -18.7C in Pershore, the Met Office said.