3Where any asset has been paid for otherwise than in cash, the cost price of that asset shall be taken to be the value of the consideration at the time the asset was acquired, but where a trade or business has been converted into a company and the shares in the company are wholly or mainly held by the person who was owner of the trade or business, no value shall be attached to those shares so far as they are represented by goodwill or otherwise than by material assets of the company unless the Commissioners of Inland Revenue in special circumstances -otherwise direct. Patents and secret processes shall be deemed to be material assets.