King took silver in a competitive men’s 110m hurdles final with a run of 13.51 seconds.
It was the sixth year in a row he has won a medal at the national outdoor championships. His collection now includes three golds, two silvers and a bronze.
He did beat favourite and former world and European indoor champion Andy Pozzi, but Windsor’s American-based Tade Ojora, who King had beaten in the heats, came through from nowhere to cause a major upset and take the title in a massive PB of 13.38 seconds.
It means no-one has yet automatically secured their spot in the 110m hurdles on the British Olympic team.
King and Ojora have the British Athletics Olympic standard of 13.38 (King has run 13.37 this season), but not the automatic World Athletics qualification standard of 13.32 to guarantee their places with a top-two finish at the trials.
Pozzi has got the World Athletics time but did not finish in the top two to confirm his spot.
King will have to wait until the World Athletics qualification period ends on Tuesday when they will send out Olympic invites to fill any quota places on world rankings, which is when the British Athletics Olympic standard comes into play.
Meanwhile, Erme Valley Harriers’ Will Battershill made his debut at the British Championships and set a new personal best to take fifth in the 3,000m steeplechase.
Battershill who took out the pace early on finished in 8:42.98.
The race was won by Battershill’s training partner Mark Pearce in 8:24.83, with Zac Seddon second and North Devon’s Phil Norman third. Seddon did qualify his Olympic spot, while Norman, who does have the qualifying time, will have to wait a few more days to find out if he is on the plane to Tokyo.
Battershill’s Erme Valley team-mate Sam Trigg-Petrovic finished seventh in the triple jump final on Sunday with a best of 15.47m.
Tamar Trotters’ Mike Wilsmore competed on the first night of the championships and came agonisingly close to reaching the final of the 1,500m.
Wilsmore missed out on a fastest losers spot by just one place with a 3:48.02 run in heat two of four.
On the same night, Tavistock Run Project’s Oliver Smart took part in the European Under-20 Championship 3,000m trail.
Smart had already run the European qualifying time but got caught up in a tactical slow race and had to settle for 12th place as the race came down to a final lap burn out.