-5 a couple of times since the start of November. That first early one caught me out, but then it warmed up again until the past couple of weeks.
I have a digital thermometer with an external sensor which I fixed on a north-facing wall of the house to avoid direct sunlight. It measures room temperature and external air temperature, and includes maximum and minimum temperature memories. I didn't realise that it also has a frost alarm so that caused a panic when it went off one cold night - I switched the alarm off after that! I think at less than £4 from Lidl it was a bargain.