@Paranoidandroidmarvin
U can’t say. I remember a few years ago we did an Easter egg hunt in shorts and T-shirts. Then one year there was snow at the same time of year.
Yes, my FB memories keep reminding me of that. I go out and visit certain work clients at certain times of year and sometimes have an hour or two to kill and one year I went for a walk on the beach, had and ice cream and got sunburnt, the second time, I had to cancel because of heavy snowfall, exactly a year to the day later. That was late March IIRC.
OP if you're in the UK, the last thing you should use as a guide to the weather is the calendar. The weather currently is quite good, beautiful for spring, but it's not impossible that we could face frost, ice, snow or simple cold, wet and miserable within the next month, such as Easter, that's often bad weather.
I remember many an Easter trip out to local beauty spots where we would have to shelter from rain or even snowstorms in doorways, under trees or in cafes.
August is also often cold, wet and Autumnal, before brightening up later in the year. In particular, I remember one year that 1 November was particularly warm and sunny.
But do you have to be all or nothing with the heating? We just have ours on a temperature setting and if the house is cold, the heating comes on, if it's not, it doesn't. Or you can boost it manually, or turn it down/off if you're not cold, away, or want to cut the cost. The calendar doesn't really come into it.