[1] In March 2015, it was announced that Lines would make his British Touring Car Championship debut with Houseman Racing driving a Toyota Avensis.

Cupra Racing formed a team of Seat Cupra TCR cars piloted by Carl Swift, Shayne Deegan, Lee Deegan and Stewart Lines and won the event by just half a second, beating Sports Prototype teams.

Tom Walker and Oliver Taylor drove the car as a points-eligible entry at Oulton Park in round six.

In 2018, Lines entered the Dunlop Endurance Championship in a Maximum Motorsport-run SEAT Cupra TCR, in Class 4, with fellow BTCC-driver Adam Morgan and later Mat Jackson.

[3][4] Lines' team Maximum Motorsport organises and, with Maximum Networks,[5] a tech-savvy communications company, heavily sponsors the VW Racing Cup[6] and operates the Dunlop Touring Car Trophy[7] alongside the TCR UK series,[8] also being one of the main sponsors.