It has been possible to downgrade the iOS prior to iOS8 - for a short time at least (I have done this). However, this is an off topic issue.
I deleted and reinstalled the software several times as previously mentioned. I'm not sure that repeated downloads would incur the same 'corruption' mentioned.
Possible troubleshooting of the exact issue and cause:
For anyone who has this issue - camera and flash/torch not working, the issue appears to be hardware related, and nothing to do with software as suggested above. It is extremely difficult to research the issue on this new Apple Discussion forum due to it's shonkiness, but there are posts suggesting to 'squeeze' the phone - at the camera area. This does in fact make the camera function for a short time (I assume loose connections behind the camera), but ultimately the camera fails again. There are also scary stories of Apple charging nearly $300 (I can't find a UK price for this) for some kind of repair, or refurb replacement possibly.
As far as I'm concerned, the camera has simply stopped working for no apparent reason during the iOS upgrade, but there is definitely a mechanical factor here, and is reported by others.
I will attempt to make a reservation with an Apple Store and will report back later with an update.