London Irish chief executive Bob Casey says the club will do all it can to ensure a speedy return to the Aviva Premiership.
The Exiles need a miracle turnaround in the Championship play-offs to have any chance of staying in the top division next season after their 32-25 defeat at the hands of Harlequins on Sunday.
Their only hope of survival is if Bedford overcome a 45-16 deficit in the second leg of their clash with Bristol and then go on to win the final - their Goldington Road ground does not meet minimum stadium criteria for the Premiership.
Casey said: "This is a sad day in the history of this great club.
"Relegation was not part of our plans, but we have to be honest, as hard as the players and management have worked, we haven't been good enough this season.
"The foundations at London Irish are in place.
"We have excellent facilities, a thriving academy programme and outstanding support staff. Unfortunately, the progress of our rugby programme has suffered a setback this season in what has been the strongest Premiership in a long time.
"We will do our utmost to ensure we return to the top tier of English rugby at the first time of asking."
Coach Tom Coventry feels his side has improved as the season has gone on, but conceded his own job is under severe threat.
They have managed to win only four of their 21 games and have conceded more points than any other team in the top flight.
He said: "It's a sad day for the club, the dressing room is like a morgue and it's hard to describe the feeling and it's a tough place to be.
"The boys gave everything but we weren't able to keep Quins at bay as they were able to break our defence too easily at times.
"Before rounds five to six, we were getting trounced, since then we've steadily improved but we haven't been good enough to finish sides off.
"There will be a big process of review, I'm responsible for the results and the buck stops with me. We've made some progress and I'd like to remain at the club and keep the present squad together."