The UK may already have the rules in place to comply but it does not in any way have the will to comply. Under the EU failure through neglect could be punished by massive fines. Out of the EU the rules can be safely ignored.
Totally fucked the quotes and formatting here, but anyway.
I am still convinced that the vast majority of the UK anti avoidance tax laws are not threatened at all by brexit. I am less convinced than i was, and won't be wholly surprised if i'm proved wrong.
The UK law (regs i think) implementing DAC6 has been repealed. For those who don't know this was an EU reporting requirement that required advisers to report certain cross border transactions often associated with tax avoidance. It didn't impose or require any anti avoidance rules. The UK will still require disclosure of actual avoidance transactions.
Personally i don't think this affects the UK authorities ability to deal with avoidance at all and saves a lot of pointless paperwork. But it does fit very neatly with you guys' narrative.