Hedley Byrne & Co Ltd v Heller & Partners Ltd  AC 465, per Lord Morris of Borth-y-Gest:
In his speech in Banbury v Bank of Montreal  AC 626 Lord Atkinson (at p. 689) said:
“It is well established that if a doctor proceeded to treat a patient gratuitously, even in a case where the patient was insensible at the time and incapable of employing him, the doctor would be bound to exercise all the professional skill and knowledge he possessed, or professed to possess, and would be guilty of gross negligence if he omitted to do so”.
To a similar effect were the words of Lord Loughborough in the much earlier case of Shiells v Blackburne (1789) 1 H.B1. 158 when at p. 162 he said:
"If a man gratuitously undertakes to do a thing to the best of his skill, where his situation or profession is such as to imply skill, an omission of that skill is imputable to him as gross negligence."’