Keighley Cougars relegated as York Knights claim final play-off place at Halifax's expense
Swinton's 22-12 win at Halifax coupled with a narrow defeat for Whitehaven against Toulouse Olympique means Keighley go down by just three points on for and against.
The Cougars appeared to be on course for survival after taking a 10-0 lead into half-time thanks to a Dan Parker try and three Oscar Thomas goals.
But inside the first 10 minutes of the second half, London wiped out the deficit courtesy of tries from Dean Whare and Iliess Macani.
Whare added his second to put the Broncos in front for the first time and the hosts were in full control when Bill Leyland scored.
Mark Ioane moved Keighley out of the relegation zone on the hour mark but Macani completed his double to leave the Cougars needing a late try to avoid the drop.
However, it did not come and Swinton completed a shock victory at The Shay to stay up at Keighley's expense.
Ben Crooks opened the scoring for Fax in the fourth minute but they found themselves 18-4 behind at the break after Nick Gregson added to Mitch Cox's two tries.
Lachlan Walmsley gave the home side hope and scored again after Rhodri Lloyd touched down for the visitors.
But that was the end of the scoring as Simon Grix's men suffered final-day misery.
Halifax began the day in sixth spot but were pipped to the post by York following a 10th win in 11 games for Andrew Henderson's side against Barrow, whose survival was confirmed following Whitehaven's 26-16 loss on Saturday.
It took York 28 minutes to open the scoring through Oli Field but they were quickly celebrating another try when Ronan Michael went over.
A Liam Harris penalty made it 12-0 at the interval and York appeared to be out of sight when AJ Towse scored early in the second half.
Ryan Johnston got Barrow on the board and they were sensing an unlikely comeback when Andrew Bulman crossed.
Ukuma Ta'ai's converted try restored York’s 12-point advantage but back came the Raiders as Tom Wilkinson scored to set up a nervy finish.
A Harris drop goal gave the Knights a two-score lead and Brenden Santi completed a 31-18 win in the closing minutes.
York will travel to Bradford Bulls in next week’s eliminators after Jordan Lilley knocked over a last-gasp drop goal to give his side a dramatic 17-16 win at Sheffield Eagles.
The result secured third place for the Bulls and dropped Sheffield down to fourth, meaning they will host London in the first round of the play-offs.
Batley Bulldogs did their bit with a 32-18 victory over relegated Newcastle Thunder on Saturday but are ultimately left to rue Monday's costly defeat at York after missing out on the play-offs on points difference.
James Meadows and Johnny Campbell both scored doubles, while Dane Manning and Elliot Kear were also on the scoresheet as the Bulldogs overturned an 18-12 half-time deficit.
Joey Leilua scored a hat-trick as League Leaders' Shield winners Featherstone Rovers rounded off the regular season with a 62-10 rout of Widnes Vikings.
James Ford's side will enjoy home advantage in the semi-finals on the weekend of October 7-8.
Doncaster will be playing in the Championship next season after beating North Wales Crusaders 18-6 in the League 1 promotion final.
Mahe Fonua, Loui McConnell and Sam Smeaton scored Doncaster's tries, with Toby Hughes responding for the visitors.