Swanwick J’s famous dictum in context, (from page 1782),

This brings me to the third and most difficult question, were there any steps or precautions that as employers the defendants or their servants ought to have taken and did not take either to protect Mr. Stokes from the risk of contracting the disease or towards detecting it at an earlier stage?

There were cited to me and I have perused some of the standard line of authorities dealing with the duties of employers towards their workmen, especially where errors of omission are alleged. These included Paris v. Stepney Borough Council, including the well-known passage from Lord Normand’s speech quoting Lord Dunedin’s famous dictum and putting what has been called his own “gloss” upon it, Morris v. West Hartlepool Steam Navigation Co. Ltd., Cavanagh v. Ulster Weaving Co. Ltd., and the dicta, obiter but still persuasive, of Devlin J. in Graham v. Co-operative Wholesale Society Ltd.; also the convenient summary of these and other cases in the sixth edition of Mr. Munkman’s useful book on Employers’ Liability at Common Law, 6th ed. (1966), pp. 34 to 47.

From these authorities I deduce the principles,

that the overall test is still the conduct of the reasonable and prudent employer,
taking positive thought for the safety of his workers
in the light of what he knows or ought to know;

where there is a recognised and general practice which has been followed for a substantial period in similar circumstances without mishap, he is entitled to follow it,
unless in the light of common sense or newer knowledge it is clearly bad;

but, where there is developing knowledge, he must keep reasonably abreast of it and not be too slow to apply it; and

where he has in fact greater than average knowledge of the risks, he may be thereby obliged to take more than the average or standard precautions.

He must weigh up the risk in terms of the likelihood of injury occurring and the potential consequences if it does; and

he must balance against this the probably effectiveness of the precautions that can be taken to meet it and the expense and inconvenience they involve.

If he is found to have fallen below the standard to be properly expected of a reasonable and prudent employer in these respects, he is negligent.

Edited for ease of reading. Formatting changed.