The fact that your company is a private limited company must be made clear with the addition of the word Limited at the end of your company name; the abbreviation Ltd may also be used for this purpose. For example: ABC Limited, or ABC Ltd.
If your company is registered in Wales, and the Memorandum of Association confirms this, you may use Cyfyngedig, which is the Welsh language equivalent of limited, or its abbreviation Cyf. For example: ABC Cyfngedig, or ABC Cyf.
Certain other types of company must have different words at the end of their name.
The name of your company is not case sensitive, the certificate of incorporation will list your company name in capitals but it is perfectly legal to use any combination of upper and lower case letters for your company name after formation, regardless of the format used on the application.