The previous coldest since modern records began in 1960 was Easter Monday in 1986, when it was -9.8°C.
But temperatures dropped yesterday to -12.5°C in Braemar, in the Highlands.
Forecasters are warning the cold spell is showing no signs of disappearing and could last well into this month.
Martin Munro, of the Met Office, said: "Having a cold Easter is not too unusual as some do fall in March, but we are seeing temperatures colder than average this year."
The record comes after March was provisionally declared the coldest since 1962 in the UK.
The Met Office said that from March 1 to 26 the UK mean temperature was 2.5°C, three degrees below the long-term average.
Snow has caused major disruption to parts of the country, including in west Scotland, where 18,000 homes lost power in Argyll, Arran and Dumfries and Galloway.
All properties affected by last weekend's severe snowfall have now been reconnected to the main power grid.
Mr Munro said the low temperatures would continue, with temperatures of about 6°C expected today in Scottish cities.
He said: "It will continue to be chilly and fairly dry, with some flurries of snow in the east of the country."