Foggy

Hi, I currently have a UK brokerage account which allows me to trade on the US Stock Market. This year the account now pays interest on cash held in both £ and $. 1. How can I calculate the £ value of the interest paid in $US? I am using the exchange rate at 5PM on the date the interest is paid into my account to give me a figure in £, Is this ok? 2. For calculating if any tax is due, do I then add the two amounts of interest together to give the total amount of interest earned? 3. Is it feasible to assume the brokerage firm will notify HMRC of these figures making points 1 and 2 above irrelevant. 4. Will the above also apply to dividends from US stocks paid into my account in $US, ie the exchange rate at 5PM on the day the dividend is paid into my account. Thank you