webstereo since you are BAEC gold (= Oneworld emerald) you are entitled to an extra 20 kg/one piece over and above the allowance stated on your E-ticket on ANY Oneworld flight. (Both BA and RJ are Oneworld members.)
Are your flights on one or two separate tickets (PNR)?.
If it is onethen the baggage rules of the first flight to cross the Middle East/Europe sub-area boundry that determines your baggage allowance. Look at
checked-baggage-allowance for some details of multi carrier journeys.
Remember that your OW weight/piece bonus is in addition to what is stated on your ticket.