I've driven that road but never ridden it. I wouldn't fancy riding it on a dark wet night even with my good lights unless I was really stuck - I'd be following the cycle route along back roads and tracks despite the extra distance.
I know others will be along to lay complete blame at the driver for not driving at a speed that allows him to spot the sheep/tree that jumps out at him, but I am a firm believer of cyclists helping themselves and obeying the law as well.
Not complete blame (the law says the bike should have been lit+reflectored), but well, a driver should be able to see unlit objects in the carriageway, shouldn't he?
Also, "he thought his lorry had hit a deer or a horse and carried on to the company’s depot" - potentially leaving a dead horse in the road for following motorists to hit?!?
"Given the weather conditions I didn’t think it was safe to pull over at that time" - why? Surely it's better that his huge well-lit lorry stops to deal with the dead "horse" than some poor old pensioner in a Ford Ka has to? Doesn't that road have fairly good visibility on the Aust-Pilning stretch anyway? No sharp bends or anything until you get nearer to Avonmouth. It feels like there's something more there - possibly it's only that lots of motorists drive too fast along there (maybe on its 50mph limit even in bad weather) but does anyone know whether Farm Foods drivers are rewarded for meeting tight schedules?
(edited to remove duplication and elaborate on why the lorry should have stopped)