In a personal injury action, is denial of a fair hearing a denial of relevant and admissible evidence a "error of law"?

I was referred in argument to the words at p. 186 of de Smith’s Judicial Review of Administrative Action, 3rd ed, (1973), where it is said that: “the rejection of relevant and admissible evidence is usually no more than an error of law, but in some situations this may constitute denial of a fair hearing according to natural justice.” In addition, I was referred to the authorities recited there, especially Bond v. Bond, [1967] P. 39, [1964] 3 All E.R. 346 (D.C.), where it was held that the rejection of evidence which occurred there arose from “ ‘a very serious misdirection which goes to the root of the case,’ that is, one which by its very nature amounts to a substantial wrong”: see p. 47.