He has continued to add to his tally ever since and reached his latest milestone by scoring two Super Saloons victories at his home circuit.
The Ford Escort WRC driver had lost out to Longfield's Nick Sutton in the second encounter but was promoted to top spot after the race when the Mitsubishi Lancer Evo 10 pilot was penalised for passing before the startline at a safety car restart.
Birley, who runs an engineering supply company, says he was not expecting to hit 700 wins this year.
"I'm really glad it happened at Brands Hatch – it feels great and was a bit surprising," he said.
"It was a shame the second race ended like it did as up until the last lap it was really close.
"I have no real target now – I will keep going for a couple more years as long as I enjoy it."
Birley, who started racing when he was 17, says he may use his BMW E36 more next season.
The 2021 season concludes at Brands Hatch this weekend with a MotorSport Vision Racing meeting featuring the IndyKA 500 event on Sunday.