Race leader Ollie Wilkinson was tagged by Auto Sport Promotion Mercedes driver Raffaele Marciello at the Dingle Dell righthander with approximately four minutes of the one-hour race left on the clock.
The McLaren 720S GT3 that Ben Barnicoat had propelled into the lead on the opening lap turned sharp left into the barriers and ended up on the banking above them in an area where there are no spectators.
The accident happened when Wilkinson and Marciello were lapping the Tempesta Racing Silver Cup class Ferrari with Giorgio Roda at the wheel.
Roda had baulked Wilkinson into the preceding Westfield corner allowing Marciello to get half alongside the race-leading McLaren.
The Mercedes-AMG GT3 Marciello shares with Timur Boguslavskiy was sandwiched between the McLaren and the Ferrari at Westfield and made contact with both cars, which ended up turning Wilkinson around.
Wilkinson was able to get out of the car unaided and walk to a course vehicle for his return to the pits.
A Full Course Yellow was immediately called, which turned into a safety car under which the race finished.
Marciello took the flag six tenths ahead of the WRT Audi R8 LMS GT3 of Dries Vanthoor and Charles Weerts.
Marciello was subsequently penalised for causing a collision, with a five-second stop-go was converted in a 40s time penalty in the final results, which dropped the ASP Merc to 17th position.
That gave Vanthoor and Weerts victory in the first of the two races at Brands on Sunday.
Marciello said: “The Ferrari wanted to let me past at the wrong moment.
“I got sandwiched between the two cars and had nowhere to go.”
Marciello had been closing down Wilkinson over the second half of the race after taking over the Merc from Boguslavskiy.
Wilkinson had a lead of just under 10s after he took the controls of the Jota McLaren from Barnicoat three laps after the Merc had pitted.
Barnicoat had been demoted from pole position to third on the grid for a driving infraction in qualifying, but got the Jota McLaren into the lead halfway around the opening lap.
The Briton passed Weerts into Paddock Hill Bend away from the start and then went around the outside of Boguslavskiy around the fast Hawthorns righthander at the end of the back straight.
He subsequently built up a lead of 20s as Boguslavskiy defended from the Toksport Mercedes of Luca Stolz before the mid-race pitstops began.
The Toksport Merc in which Stolz is joined by Maro Engel took the chequered flag in third place.