The manhole (also known as lots of other terms including person hole, maintenance hole, access hatch) to your roof space can be a huge source of draughts with hot air coming into your home in Summer and warm air leaving your home in Winter.
They're easy to fix with some compression draught-proof tape. If you've got a hinged access hatch - draught-proof it like a hinged door as seen in this video.
While you're up the ladder you might also like to insulate the manhole cover and have a look around to check insulation and any other draughts such as this sneaky one.