In 2005, I was attacked and injured by a family member. I retaliated, striking back once with a slap to the side of the head. I didn't press charges, but 2 weeks later was arrested. After an investigation I was "let off" with a caution for Assault occasioning in Actual bodily harm, which the police told me "would only remain on my record for the next five years, but will count strongly against me if I'm involved in anything like this again in the mean time".
Earlier this year I applied for a job requiring an advanced CRB and it was still on there, so I phoned the offices that deal with them and they told me that in 2009 the law was changed so that people can no longer appeal to have the caution removed. That any offence, reprimand, caution or conviction must remain on file untill the person's 100th Birthday.