Congratulations on receiving an unconditional offer letter from London Met University! The next step would be to accept the offer by following the instructions provided in the letter. You may also need to provide additional documents or complete other requirements, such as paying a deposit or arranging accommodation.
Regarding your question about the chances of having a second interview to get a CAS (Confirmation of Acceptance for Studies) letter, it is difficult to say as each University has its policies and procedures. However, if you have already received an unconditional offer, the University may issue a CAS without needing a second interview.
It would be best to contact the University's admissions team directly and inquire about the CAS process and any additional steps that you need to take to obtain it. They should be able to provide you with more information on their specific policies and procedures.