The commonest collision types involving cyclists are of the vehicles pulling out from junctions and turning into junctions variety. These cut across the path of the cyclist as they proceed forward. Getting hit from behind is, thankfully, still a far less common type of collision. However, on unlit country lanes things are a bit different. Getting hit from behind is still unlikely, but it is ranked far higher (near the top, IIRC) as a causal collision type (unlike in urban environments where it is very low on the list). Unfortunately, due to increased traffic speed (NSL roads etc) they are invariably KSI casualties.
It’s also worth mentioning that cyclists are often involved in crashes and collisions where they are the only vehicle involved and are proceeding forward. The causes of these types of crashes are manifold but, ice, diesel, painted white lines, drain covers, wet leaves, too much speed, and not paying proper attention must account for a high proportion of these incidents. A rear light won't help with any of these issues, but a front light just might.