Rule 54 of The Probate and Administration Rules: Evidence as to due execution of written will

(1) Where a written will contains no attestation clause or the attestation clause is insufficient or where it appears to the court that there is some doubt about the due execution of the will, the court shall, before admitting the will to proof, require an affidavit of due execution from one or more of the attesting witnesses or, if no attesting witness is conveniently available, from any other person who was present at the time the will was executed.
(2) If no affidavit can be obtained in accordance with subrule (1) the court may, if it thinks fit having regard to the desirability of protecting the interests of any person who may be prejudiced by the will, accept evidence on affidavit from any person it may think fit to show that the signature on the will is in the handwriting of the deceased, or evidence of any other matter which may raise a presumption in favour of the due execution of the will.
(3) Before admitting to proof a written will which appears to have been signed by a blind or illiterate testator or by another person by direction of such a testator, or which appears to be written in a language with which the testator was not wholly familiar, or which for any other reason gives rise to doubt as to such testator having had knowledge of the contents of the will at the time of its execution, the court shall satisfy itself that the testator had such knowledge by requiring an affidavit stating that the contents of the will had been read over to, and explained to, and appeared to be understood by, the testator immediately before the execution of the will.
(4) If the court, after considering the evidence—
(a) is satisfied that a written will was not duly executed, it shall refuse probate and shall mark the will accordingly;
(b) is doubtful whether the will was duly executed, it shall make an order for hearing and give such directions in regard thereto as it deems fit.