Temperatures plummeted to the coldest on record for November in parts of the UK overnight.
Northern Ireland hit a new low of -9.5C (15F) at Lough Fea, Co Tyrone, and in Wales, a record minimum of -18C (0F) was reached at Llysdinam, in Powys.
Heavy snow is still falling in much of Scotland and north-east England, bringing travel disruption, and is set to last until Tuesday.
Forecasters says Siberian winds from Monday will make it feel even colder. Met Office severe weather warnings for heavy snow and widespread ice remain in place for eastern Scotland, and eastern England from the Borders down to the East Midlands.