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 would have done what he did even if he had not had the information.1
In this scenario, the onus is on the defendant to prove that he would have dealt the securities regardless of the inside information. This may be easier to prove if the defendant can demonstrate a pattern or a regularity in his dealing behavior or a documented trading strategy.
1 Criminal Justice Act 1993 (CJA), c. 36, § 53(1) (UK).