If your company was formed on or after 6 April 2008 then under the Companies Act 2006 it is no longer a legal requirement to have a secretary appointed.
If you are registering a new company then there is no requirement to appoint a secretary at the time of incorporation. All you need is one director to be appointed. The responsibilities of the company secretary will then automatically be passed to the sole company director.
Many companies are now registered with just one single person as the sole director and sole shareholder. Even if you have two or three directors appointed you do not need to make one a company secretary.