I can't comment on the UK; I'm in the US. I work in the pharma industry--insider trading is possible for me on a daily basis. I could have been a zillionaire by now if I did it.
If you figure you won't get caught, you are most likely right. But the problem arises if someone complains. One of my company's clients complained, for example. They were within their rights; considering the action in their options a few days before one of their announcements, I think it is very possible that there was some insider trading, although I doubt that anyone in my company did it. Based on their complaint, the securities regulatory agency asked our company for the names and social security numbers of everyone who works there. These were "voluntarily" disclosed. From there, they can go to your tax return. And if they see anything on the return they don't like or there isn't enough information for them there (here you can write "various" if you have traded a lot of stuff), they can subpoena your trading records. In the US, I am sure the broker would cough them up with or without your consent.
You don't want to go to jail, do you? Buy yourself some mutual funds. Freedom is more important than money.