Thanks to Rob, Heart of A Lion and Trinakrian for your input.
Sorry I didn't reply sooner, I had a blown psu due to a crappy coolermaster psu and a brownout combo (not my week.) You caught me Trinakrian, I usually do check, but this time I was complacent and didn't check the update notes regarding setting the graphics driver before performing this update

Unfortunately, I've tried all of the suggestions from everyone in this thread and still can't get to a login. Thankfully, I do have a complete backup that I will restore as a last resort, but since I have another computer to work with I'll continue to try and troubleshoot this and/or wait it out.
Some of the things I've tried:
-removed and reinstalled my nvidia drivers to no effect.
-tried to use the nouveau drivers and it made no difference, still got stuck on a black screen at login.
-reinstalled xorg, lightdm
-installed vertex themes and made the required changes to gtk greeter settings conf
-Tried to use lxdm to login instead of lightdm
-Tried various different kernels
Despite all this, still stuck at the same black screen at login. Thanks again for all the suggestions, a great community you've got here.
Peace