Information Powers: TMA70/S20: Definitions: Documents in his Possession or Power
Documents in the person’s possession or power are existing documents which are in the person’s possession or which he can obtain, and not documents which he can cause to be brought into existence.
Provided there are reasonable grounds for believing that a document is in a person’s possession or power, the onus will lie with that person to demonstrate that they do not, in fact, have possession of or power over the document (see the Special Commissioner’s reasoning in paragraphs 53 onwards of his decision in Meditor Capital Management Ltd v Feighan SpC409).
That case was an appeal against a CTSA information notice under Para 27 Sch18 FA1998.
There is no appeal mechanism for Section 20 notices. However, similar principles will apply to representations about possession or power received in response to a S.20B(1) opportunity letter. You should seek supporting evidence before accepting that the noticee does not have the power to provide the information. In the absence of such evidence it will probably be appropriate to pursue a notice or penalty proceedings for failure to comply with a notice already served.