London Irish's relegation from the Premiership was confirmed on Sunday as Bedford Blues suffered defeat to Bristol in the Championship play-off semi-finals.
Defeat to Harlequins last weekend meant Irish were certain to finish bottom of English rugby's top flight.
The Exiles retained slim hope of avoiding a first relegation since 1994 due to Bedford not meeting Premiership entry criteria.
However, the Blues were comfortably beaten by Bristol over two legs, the latter triumphing 45-19 at Ashton Gate on Sunday to wrap up a 90-35 aggregate win and book a promotion decider with Doncaster.
Doncaster were beaten 17-14 at home by Yorkshire Carnegie, but that was enough to earn a 44-34 aggregate triumph.
Defeat for Carnegie brings an end to the career of Kevin Sinfield, the 35-year-old having switched codes last year after a glittering rugby league career with Leeds Rhinos before announcing he would retire last month.