In Accurist Watches v Wadher, the Employment Appeal Tribunal (Underhill P) has held that although evidence is required when considering an application to extend time, it need not be in any particular form. Specifically it need not be in the form of oral testimony from the Claimant.
Distinguishing a previous EAT decision where it was said that no extension could be granted without evidence from the Claimant, Underhill P clarifies that actual testimony is unnecessary (although it is, of course, desirable). It is sufficient for a tribunal to rely on medical evidence, or even infer facts from pleadings or contemporaneous documents (paras. 16-17).