You may remain silent, not make a statement and only reveal your defence for the first time in Court. However, if you do so, there is a danger that the Judge may think you have subsequently made up your defence and can decide not to believe you. However, if you have already made a statement of the facts that support your defence, spoken at length to the investigating officer, and made numerous witness (long) statements over many days, your silence may not necessarily be disadvantageous to you.
What is a Cautioned Statement?