Right now i believe that its is easier to hide BTC than anything else.
But with ONE simple rule, you have do it right from the start.
Do not use excahnge , because in with any notable amount you will have to submit ID or something .
My view is that if individual buys btc on localbitcoins or from a "BTC dealer " it is very hard to find out that he did .
As ever though most people only think of these things when it's too late. When you're fully loved up you'll go straight to Coinbase and give up every shred of anonymity. Convenience trounces paranoia 9 times out of 10.
I'd very curious to know how many husbands or wives have informed their dearest about their crypto. And I also wonder how carefully bank records are gone through when it comes to divvying up finances. I assume they're not going to bother unless you're suspected of something.
By the time most divorces come to pass you might have bought in more than seven years ago in which case bank records can't be retrieved in the UK. If you kept your mouth shut you might stay in the clear.
I will never get married so will never have this problem.