If the goal is to pay tax in Hong Kong or UAE at lower rates than UK and you are actually living there and not in UK, it will most likely work. You may even consider a private letter ruling. I am aware of companies that did this, not with UK but other two countries.
If you start using nominee directors, you will most likely run into troubles once you have an audit. The tax guys in Europe are known to audit companies at the place of management and ask questions to the directors. If you have some random dude there, it will cause troubles.
If you do not report or pay tax in Hong Kong, it will be considered tax evasion in the UK and not Hong Kong. This is also one of the reasons why foreigners doing business in China always pay full amount of tax there while the locals are less tempted to pay the full amount. Also beware that even Hong Kong tax audits and investigations are no longer just on paper, they actually start chasing your tax. Hence, I do not think that not paying tax in UK and then claiming offshore in Hong Kong will work very well. This because the conditions to claim offshore most likely contradict the requirements of the DTA to not pay tax in UK.
The currency is generally not a problem. You must simply convert your profit, turnover, etc. to the local currency at rates given by the tax authorities. Hong Kong recommends to keep the books in the relevant currency, which may be USD or something else. I would recommend you too. Imagine, you have 10M GBP assets and do little trade. If your books are in HKD, your profit or loss goes up and down each year just based on the fluctuating exchange rate, distorting your real profit. If your books are in GBP, your profit is what you actually earn.
Also note that for the case in Hong Kong, you will get around the mandatory CPA audit.