In the UK I believe it's possible to agree a salary/payment at an amount of recognized currency, such as GBP or USD, and then you perform all your tax and related calculations based on that. How the payment is actually transferred is, potentially, up to the people involved.
I believe that I can contract my services at, say, 100 GBP per hour, bill for one hour, and then accept payment in bitcoin, stating that there is an agreed rate of exchange. If the stated underlying rates are not regarded as "unusual" by the HMRC then most likely the arrangement would be permitted to stand.
There are laws concerning "payment in kind" and I think this would fall under that. Note, I'm not an accountant or lawyer, but I've seen barter arrangements not dissimilar to this accepted as valid by HMRC.