Most income that arises in the UK is taxed by the UK after the £12,570 single persons allowance.
So you would pay tax on pension income over that figure, interest on cash, dividends, bond coupons etc.
However if officially non-resident for tax you don't pay any capital gains other than on property so profit from share sales for example are not taxed.
If you have income offshore and are non resident then that income is not taxable by HMRC.