For 1999, Aïello switched to the British Touring Car Championship (BTCC), driving for the works Nissan team in their Primera model, replacing the outgoing Anthony Reid, whom had moved to Ford. He had initially been offered the drive at Renault, but rejected the offer as WilliamsF1, whom ran the team, refused to allow him to enter the 24 Hours of Le Mans. The season would prove to be highly successful, as he took the title in his one and only season in the series, with 10 wins helping him finish 16 points ahead of teammate David Leslie, and Nissan taking a comfortable Manufacturer's and Team's championship victory. His performances in the BTCC saw him win the National Racing Driver of the Year award in the Autosport Awards. He also entered the 24 Hours of Le Mans in 1999, this time for Audi in their Audi R8R, and he finished third in class.