I live in England so a pretty moderate climate and don't expect temperature to play a factor. The windows are not near the radiator in the room and I have certainly not made an impact on it.

Despite me telling the landlords months ago they are only just doing something about it now (as we are moving next week) and inevitably they are going to blame and bill this on me.

There is a crack in the wooden frame of the window, which the second and third image highlights. Does this have anything to do with it?

I was wondering if anyone else could explain why this crack has appeared out of nowhere. Thanks!

Could you post a couple more pictures, please?

Pictures looking straight (90 degrees to the face of the glass) at the window centered directly on the crack origin point - right where it comes out of the sash edge.

At least one picture about 5 cm away from the glass and one about 50 cm away.

There are various reasons why glass breaks, thermal breakage being just one of them. My immediate reaction is that your break isn't thermal stress for a couple of different reasons.

You have a very high stress break, so if you can post those additional pictures it might help to determine what happened.

Thanks!