I called customer services tonight and they said they couldn't access or change any info on my policy as it has been locked on the system by the Underwriters.
Kinda bricking myself....can't see them being bastards over a date I got wrong. If I was going out my way to hide information I wouldn't have told them about it!
The number on the letter closes at 6pm, so I got the number off the website and called them and they confirmed the 'audit'. So it is definitely from Admiral. It wasn't the date of the accident I got wrong it was the date of my conviction on my driving license.
Whilst I see no harm in confirming dates with them etc etc, I would point blank refuse to send them any bank statements.