You may be unsure when applying which most appeals to you. Use the UCAS code which shows your main interests. If you mistakenly do apply using more than one course code within a faculty and are made an offer you will be made the same offer for all courses. If you are made a conditional offer to more than one course in the Faculty you should not accept both a firm and insurance choice in the same Faculty as the entry requirements are likely to be the same. When admitted you may have a free choice of courses within that degree area, subject to the approval of your Adviser of Studies, provided you are suitably qualified.
Psychology has a restricted entry system.
Unless you apply for and receive an offer using a UCAS Psychology code you will not be considered as a candidate for Honours level Psychology, although it MAY be possible for you to take Psychology courses as an outside option subject to demand each year.