7(1)A requirement under paragraph 4 or 5 to return a travel document in the possession of a constable or qualified officer does not apply while the constable or officer has power to detain it under sub-paragraph (2).
(2)The constable or qualified officer may detain the document—
(a)while the constable or officer believes that it may be needed for use as evidence in criminal proceedings, or
(b)while the constable or officer believes that it may be needed in connection with a decision by the Secretary of State whether to make a deportation order under the Immigration Act 1971.