The Met Office said Katesbridge in Northern Ireland had seen its lowest temperature ever recorded in May on Thursday morning at minus 6.1C (21F).
Previously the area had recorded a record low for May of minus 5.2C (22.6F) in 1995.
The freezing temperatures were almost as cold as Northern Ireland's record low of minus 6.5C (20.3), recorded in Moydamlaght, Co Derry, in 1982.
The UK woke up to freezing weather as sub-zero temperatures were recorded overnight.
Temperatures in Shap, Cumbria, dropped to minus 4.6C (23.7F) overnight and in North Yorkshire minus 4C (24.8F) was recorded.
But they did not get close to the lowest temperature ever recorded in May for the UK, which was minus 9.4C (15F), in Lynford, Norfolk, in 1941.
Met Office spokeswoman Nicola Maxey said temperatures would pick up through the day and warmer weather would be on the way for much of the country in time for the weekend.
She said: "We are slowly seeing day-on-day warming and we are seeing temperatures pick up, certainly by Sunday in London when we'll see temperatures of 20 or 21C."
