Thanks both for advice..
Yes ISPs do say to leave them on, but it is always my habit to pull plugs out at night before bedtime.
I know the fridge and freezer is obviously left plugged in, but I was a bit wary of leaving the router on. As stories I have heard on the news about mobile phones being charged overnight has caused fires.

Very unlikely, Margaret. In fact, I believe the advice from ISPs is to leave them on. However, they do benefit from being switched off once in a while to allow them to reset themselves.

I tend to leave my router on all of the time, and have no problems with it at all.

I was wondering if leaving the router on all night it will cause it to overheat.
I always pull plugs out before going to bed. But I got scoffed at by someone online when I said I don't like leaving my router on all night.