I am not an expert but I think that even trading on a leak is not unlawful as long as that leaked information was indeed made public (e.g. someone leaks to the media and the media then publish it), although it may have been unlawful to leak the information. The point is that insider trading is not allowed. It is no insider trading if the information is available to everyone.
Yes, I have had the corporate training on leaks and insider trading, too...
Trading on public information is fit and proper (Edit: Indeed, a technical term, but that does not make my statement incorrect, or does it?)
I think you may have skipped the part of leak to whom. If it is a leak to you then it is still not public and indeed insider trading. But if leaked to the public then it is different (and also how do you prevent people from trading on what they see in the media?)
But that's in general as in this case, the OBR admits they released it and, again, anyway once it's on BBC News it's free for all.
Well if you are an expert that's great as you will be able to explain how using a leak to the public and/or something that is public information can be construed as improper. That was my previous point and question.
I agree. They didn’t intend to publish it, but they did publish it. They might not have advertised its presence yet, but it was freely available to anyone who asked.
the effects are not minimal
if you're crooked: getting this sort of information early is potentially extremely lucrative
(why crooked? because trading on UPSI is illegal)