Under the CJA, a person is not guilty of insider dealing by (i) virtue of dealing in securities and/or (ii) encouraging another person to deal in securities if he believed on reasonable grounds that the information had been disclosed widely enough to ensure that none of those taking part in the dealing would be prejudiced by not having the information.1
This is a defense against the disclosure offense, but it would be difficult to rely on where a security is traded on a regulated market because of the requirement that none of those taking part in the dealing be prejudiced by not having the information, which is difficult to prove. It is also likely that those who try to rely on this defense will still have committed the offense of encouraging another to deal while in possession of inside information.
1 Criminal Justice Act 1993 (CJA), c. 36, § 53(1) (UK).