Rule 123
Conservation of evidence

(1) On request, the European Patent Office may, without delay, take measures to conserve evidence of facts liable to affect a decision which it may be called upon to take with regard to a European patent application or a European patent, where there is reason to fear that it might subsequently become more difficult or even impossible to take evidence. The date on which the measures are to be taken shall be communicated to the applicant for or proprietor of the patent in sufficient time to allow him to attend. He may ask relevant questions. 

(2) The request shall contain: 

(a) particulars of the requester as provided in Rule 41, paragraph 2(c);

(b) sufficient identification of the European patent application or European patent in question; 

(c) an indication of the facts in respect of which evidence is to be taken; 

(d) particulars of the means of giving or obtaining evidence; 

(e) a statement establishing a prima facie case for fearing that it might subsequently become more difficult or impossible to take evidence. 

(3) The request shall not be deemed to have been filed until the prescribed fee has been paid. 

(4) The decision on the request and any resulting taking of evidence shall be incumbent upon the department of the European Patent Office which would have to take the decision liable to be affected by the facts to be established. The provisions with regard to the taking of evidence in proceedings before the European Patent Office shall apply.