How can my son clear his UK police arrest record?

Seven or eight years ago, my son was arrested with his friend and accused of raping a minor. This minor is like some girls nowadays; dresses older than she is and drinks, smokes, and behaves sexually promiscuously, and is allowed to stay out all night. My son and his friend got drunk along with the girl, and ended up at my son's house. He went to bed and left them downstairs, but she alleged rape against both of them the next day and both were arrested. The charges against my son were dropped; he gave a DNA sample but the police decided that there was no case to answer; there was no matching DNA at his house (and believe me, he wouldn't have tidied up...) and he was released without charge. However, he was stopped on his way home from the pub last night in a different area entirely, and the policeman did a background check on him; because of that he then became a person of interest to them because of robberies in the area, purely because he had this arrest on record. Now, I'm aware that every mother thinks her son is a good kid, and I'm no different, but he wasn't in trouble with the police before that event, and hasn't been since. IF he can, HOW can he get his arrest record cleared? Isn't there now some procedure he can follow?