Once you have been non resident for a year and a day, you are no longer liable for UK tax on your worldwide earnings or capital gains. You generally become ordinarily resident in the UK 6 months after your return but it could be sooner if you clearly have 'intent to settle'.
You will not pay taxes on money you earned whilst you were non resident even if/when you return to the UK. Does not matter where that money is held. Capital is not taxed in the UK. Well for now, under a Goblin government we could get a wealth tax. Until then you will only be taxed on income, capital gains, dividends or interest earned AFTER you have become ordinarily resident.
If you want to continue to pay no tax even after you return, you will have to be classified as a non-dom.
The UK authorities will know you were working overseas because you were not resident for tax purposes.
The UK authorities do not care where you worked overseas or how you spent your money. If, after you return, you try to hide your assets to avoid paying capital gains, you will be caught.. All countries cross report. So, for example, when I ceased being resident in Switzerland I had to give my Swiss bank my address to the UK. UK tax authorities were immediately notified by the Swiss authorities. As I was not ordinarily resident in the UK it did not matter but had I been resident, the tax man would have been at my door pdq.