The business made a profit of £525m last year on the back of a record £47bn places on bets.
Last year Coates topped the economia Accountancy Rich List.
She trained as an accountant within her family’s chain of Midlands betting shops. Coates asked her father Peter to let her run the chain and expanded it to almost 50 stores. In 2000 she decided the future was online and mortgaged the shops for a loan, buying the Bet365 domain name for $25,000 on eBay.