The aircraft was landing on Runway 26 at Bournemouth Airport. The weather was fine, with a surface wind from 310° at 11 kt. The aircraft touched down on the runway centreline but immediately deviated to the left. It ran off the paved surface onto the adjacent wet grass before the pilot was able to regain directional control through rudder pedal application and use of the right side wheel brakes. The pilot steered the aircraft back towards the runway, but as it crossed back onto the paved surface the nose landing gear encountered a slightly recessed drain and collapsed. The pilot noted that, as the aircraft was being recovered, the left wheel brake appeared to be binding. This, combined with the aircraft’s behaviour at touchdown, led him to believe that the aircraft had touched down with undemanded partial left brake pressure applied.