If you buy yen for gbp, yen value goes up, gbp goes down.
If you tip a glass of water into the ocean, the level in the ocean goes up, the level in your glass goes down. Bitcoin is no different to, say, gold in the respect of being outside the fiat currencies.
The illegal drug market is the 3rd largest industry in the world, if major players in this realise...
I'd imagine that if "the major players" know anything at all about Bitcoin right now, it's that it has properties that make it useful for black market dealings. That's pretty much the first thing people seem to hear, unfortunately.
Keep as much as you can in the bitcoin world, then you only need to declare whatever you have changed into fiat cash, maybe so little that you don't have to pay any tax at all.
That throws out the baby with the bathwater, doesn't it? Admittedly a large proportion of your tax goes on defence and military spending, but you're also paying to have your rubbish collected, have your community centres maintained, have the courts run...