Do you leave your heating on overnight
No. If it's really cold it might come on during the night, but it's kept in the warmest part of the house, so rarely does.
Neighbours have probably turned their heating off, using yours that is creeping through the adjoining walls !!.
Funny you should say that. Some of our internal walls that we share with one side are only single skin and in one room only a stud wall (the house was split in along it's length some time in the early 20th century). Neighbours had a leak once and it came along their floor boards and under our shared stud wall.
Barry replying in his vest and boxers
It's my default look these days.