McGhee v National Coal Board [1973]

Pursuer developed dermatitis.
Allegedly caused by employer’s lack of washing
facilities at workplace.
Medical knowledge unable to put figure on how much
this increased the risk, only that it did.
Therefore med evidence unable to establish breach as
probable cause.
House of Lords held that in absence of complete
medical knowledge there was no substantial difference between materially
increasing the risk of injury and
making a material contribution to injury.

Therefore pursuer succeeded.