Championship title contenders Bristol, Yorkshire Carnegie and Doncaster have all met minimum standards criteria that would allow them to play in the Aviva Premiership next season.
The trio, plus Bedford, will compete in the opening round of Championship play-offs this weekend, with the final taking place over two legs next month.
Bedford, though, did not apply to have their ground audited and would not be promoted if they win the Championship.
That means the Premiership's bottom club - currently London Irish - would not face relegation, but only in the event of Bedford being crowned champions.
Irish are set to finish 12th and last if they lose against Harlequins on Sunday, but even a win will not be enough if Newcastle triumph at Premiership leaders Saracens.
A statement issued on behalf of the Championship said: " The Rugby Football Union (RFU) has considered the findings of CSM Strategic's independent audit report of the Greene King IPA Championship semi-finalists, assessing their eligibility for promotion to the Aviva Premiership next season.
"Bristol Rugby, Doncaster Knights and Yorkshire Carnegie have met the minimum standards criteria to the satisfaction of the RFU, based on the following stadia: Ashton Gate (Bristol Rugby), Headingley Stadium (Yorkshire Carnegie) and Keepmoat (Doncaster Knights).
"Bedford Blues did not apply for the audit and therefore cannot be promoted to the Premiership."
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