Questions about interest from US Treasury Bill wait for maturity

I have below two questions related to interest from buying US Treasury Bill (Zero coupon) and wait for maturity: Q1: when calculating the interest received by buying a US Treasury Bill (zero coupon) and wait for maturity, which one of the below is correct? (a) do we need to convert both the buying price and maturity price from USD to GBP individually (using USD.GPB currency conversion rates) to calculate the differences? Or (b) calculate the differences of buying price and maturity price in USD, then convert to GBP at maturity date? Q2: for buying a US treasury bill (zero coupon) at 2 different times and sell part of this bill and the rest wait for matured, which one of the below is correct when calculating the interest of the part wait for maturity? (a) to use the Section 104 pool price in GBP to calculate the interest part of waiting for maturity? or (b) use the average buying price in USD to calculate the interest then convert from USD to GBP at maturity date? Thanks.

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 .