Negative income after currency exchange

Hi, I have exchanged HKD to USD in Interactive Broker to buy US treasury bills. Understood the gains from the bills should be counted as foreign income in self-assessment. However, because of currency loss, the gains become negative after being converted to GBP. Do I have to declare the negative gains in self-assessment in this case? Thank you.

Hi,
US government bonds, sometimes known as T-bills or treasury bills are generally taxed as income rather than capital gains.  
The return is paid at maturity rather than regular interest payments.  
In the UK, these are known as deeply discounted securities, with the discount being the difference between the price at which they were issued and
the price received at maturity.  
On a foreign investment the income is the difference between the purchase and redemption price after each has been converted to sterling on the day the transactions took place, so includes any foreign exchange gains.  Losses cannot be deducted. 
Have a look at SAIM3010 - Deeply discounted securities: introduction for more information. 
Thank you.