Re: I am not sure of the law in various parts of the world where microsoft operate
"Given that, in many cases, this is likely to fill the hard drive and stop the computer working it is no better than a virus and MS will have to pay for this bigtime."
Not really. Yes there will be a small amount of users who use a small drive or small partition for the OS who will have issues. I guess they will have to be extra vigilant or adjust sizes to suit. Unless someone is ghosting the OS drive every night and retaining copies (why???), I cant imagine this would be an issue. Mr Average will have a store bought Win7 or Win 8 pc and I doubt that there will be many who cannot spare 3GB of storage space. I doubt they would even notice the increase in footprint.
The significant issue here is that this download (which is effectively forced on you) may cause you to exceed an ISP download cap which in some cases may cause a financial or speed penalty to your connection.
Sure, you can set your connection to metered and Windows 10 is pretty effective at detecting metered connections but those not using wireless who have a metered connection will have a problem here.