A Bestinvest account number always begins with the letters 'BI' followed by a series of numbers. You can find it on the email we sent when you opened your Bestinvest account. If you need help, call us on 020 7189 9999. Our helpline is open 7:45am to 6pm on weekdays (8pm on Thursdays) and 9:30am to 1:30pm on Saturdays.