Ok I found the fix for the HP Printer and W10 updates failing.
I posted this on the HP forum, if you're having problems follow what I wrote here;
I've done this on 2 PC's.. W7 to W10, and W8.1 to W10.
What you have to do is;
1. Go to device manager. Look down the list for Printers. Open up that arrow and see if you're printer is listed there?
If it's listed as Unknown Device then;
2. Go to the HP website and find the driver for your printer on there. Download it through the website / program as though you was installing your printer for the first time i.e. it should check the connection of you're printer during this process.
3. Now you have your printer driver re-installed. Go back to Device manager and check that it now appears listed by the correct name in the Printer section.
3a. If there are other unknown devices besides your printer listed, you need to delete the other unknown devices, leaving only your printer listed.
4. Go back to windows update and retry a windows update (it asks you to install the old failed ones first, so try it, expecting failure, then press the retry button.
5. If all went well, it shouldn't list anymore updates, and you're done!