Thanks you both, appreciate your replies. I have checked the flange of the door, nothing in there… However, reading more into the properties of rust, I am less sure that it is rust now. The only thing we have found to get/ rid of it is bleach, but apparently bleach would not work on rust Why You Shouldn’t Use Bleach to Clean Rust Stains (lifehacker.com). I have no idea what else it might be though.
Also, we are not using a tumble dryer to dry the clothes. The stains are there straight after taking out of the washing machine, so it is definitely the washing machine causing it.
I am tempted to buy a new machine, although even then I am not certain it is the machine itself rather than any of the pipes coming into the machine, so no guarantee that would sort it…