It is not stated specifically in Section 1 of the Act that the police can search an object/article that the person is carrying, pushing or pulling.
But...
Think about it like this. Section 1 of PACE states that a constable can stop and search a person for prohibited articles. What does "search a person" actually mean? It means search the clothing that the person is wearing, or to put it another way, search the possessions that the person has with them at the time. Does the person 'possess' a coat and does he have it with him at the time? If yes, the coat can be searched, etc.
�Search a person� in reality means �search the possessions of the person that they have at the time of the stop search�. This includes anything they are wearing, carrying, pushing or pulling at the time.