Is there really a measureable chance of some CAA official accessing a pilot's logbook, auditing the entries, cross-referencing those to a separate audit of an aircraft's insurance, and then pursing a case against the pilot?
No, there isn't. There is however a good chance that a concerned observer might inform the CAA of their concerns, watching an aircraft fly without insurance, or overhearing someone having a conversation which is clearly going to invalidate insurance and therefore C of A.
Having personally been involved in investigations of this nature, I can tell you it's not fun, there are certainly no tea and biscuits when the investigator thinks you've done something wrong, and having something illegal in your log book is certainly not going to go in your favour.