The CPS confirmed to the BBC earlier today it would be reviewing the file's contents.
Twenty-one people died and 220 were injured when bombs were detonated in two city centre pubs in 1974.
West Midlands Police has not identified the individual at the centre of the file.
Monday marks the 48th anniversary of the bombings.
Inquests in 2019 highlighted the role of the IRA.
Nobody has been prosecuted since murder convictions for six innocent men – the so-called Birmingham Six – were quashed in 1991.
Campaigner Julie Hambleton, the sister of Maxine Hambleton who was one of the slain 21 and a key member of the Justice4the21 group, told the BBC she hoped the CPS would look at the file "as a matter of urgency".
"It is 48 years after all," she added.
"We hope that our loved ones will finally get a door opened for them to have truth, justice and accountability."
Ms Hambleton and her family have brought a civil case for damages in connection with the attacks.
She said she remained "cautiously optimistic at best" about the latest development.
"If it had happened ten years ago I would have been very encouraged," she said, explaining hope had since been tempered "because we've been let down so many times".