The "insider trading pound sterling" claim isn't just less interesting. Whoever put that in the complaint should get Rule 11 sanctions for making frivolous allegations.
TIL: there is no Rule 11 equivalent in the Federal Rules of Criminal Procedure. Interesting discussion at United States v. Aleo, 681 F.3d 290, 308-09 (6th Cir. 2012) (perish the thought that a prosecutor could get sanctioned for filing a frivolous pleading that would get a civil litigator Rule 11'ed).
The author alludes that the traders would have been making those trades "all day", but suspiciously absent is any evidence that they actually had. According to the facts reported, the traders only traded pounds on three days over a week-and-a-half period.
We need to see the traders' trades for a longer period before the Cairn trade to see if they actually do trade pounds all day.
The person arrested was "global head of foreign exchange cash trading". Is it normal for global heads to be making routine trades all day? (the article indicates it is not; again, only three trade days out of 10+)
From the article it sounds like this person was more involved in client relations/sales than technical execution.
By the same token though, the entire FX book is under his jurisdiction, so it wouldn't have mattered if he'd delegated to another trader (except that it looks more culpable this way).
Surely some federal rules of criminal procedure equivalent.