What is the test for setting aside a judgment signed in default of appearance?

[12] The cited case of Evans v. Bartlam [1937] A.C. 473 expands further on the above foundation as follows (page 481-482): “The contention no doubt contains this element of truth, that from the nature of the case no judge could, in exercising the discretion conferred on him by the rule, fail to consider both (a) whether any useful purpose could be served by setting aside the judgment, and obviously no useful purpose would be served if there were no possible defence to the action, and (b) how it came about that the applicant found himself bound by a judgment regularly obtained, to which he could have set up some serious defence. But to say that these two matters must necessarily enter into the judge’s consideration is quite a different thing from asserting that their proof is a condition precedent to the existence or exercise of the discretionary power to set aside a judgment signed in default of appearance.”