Trying to get away from Windows completely. :)
sudo lsusb reports the dongle as 12d1:1446 (one web site I found (kerry-linux.ie) lists 12d1 as vendor-id ID for Huawei dongles in general regardless of size).
I changed the script above to 12d1, removed the dongle and re-inserted it: still got the "disk" listing.
Closed the laptop, re-opened it with the dongle still installed, logged in, same situation.
I notice the product ID on the above site varies for different products within the huawei range - none of them are 2000 so I have changed that to 0x0001 - still no change.
Went into root and ran a script I got from another site, re-creating ttyUSB0 first, using the default vendor and product IDs and those mentioned above in a call to modprobe usbserial - I'm getting demoralized now!
I think part (all?) of the problem may be not having the correct product ID. The Huawei website does not even recognise e353 (the code the dongle was sold under) and there is almost no relevant information in the windows setup scripts.
One thing I have noticed whilst trying to get this dongle to work: the computer has locked up several times - virtually unknown before this. :(