thanks for reply. 'Seems reasonable but you do take on some FX risk even though the HKD is pegged to the USD it does fluctuate.' I totally agree, there is risk in the FX trade, and that can go either way and l'm ok with that. l may lose substantially more than the nominal interest gains, but may also gain more to supplement the nominal interest gains, when l actually need the currency denomination, which is ultimately GBP, sterling. But if l leave the currency, HKD, in my Hong kong bank, it is only losing. and the inflation rate for HKG is likely greater than US, certainly for property! its like that for HKG banks, they don't pay any interest, no matter what the inflation rate, they want you to invest in mutual funds etc. so out of the 2 choices, leave in HKD and earn 0% or put it in USD or ZAR and earn ~ 0.6% and 6% respectively?
makes sense and given your rate it sounds like you're using IB where the FX spread for HKD is usually 1/10 of a pip you don't have much slippage going back and forth.