Only 52,000 asylum cases out of a backlog of about 450,000 have been processed by the Home Office since last year, the BBC has learned.
The problem of the backlog came to light in July 2006.
The details were disclosed in a letter by the chief executive of the Border and Immigration Agency, Lin Homer.
The backlog of 400,000 to 450,000 electronic and paper records of asylum seekers was revealed by the previous Home Secretary, John Reid.
He told parliament the records were "riddled with duplication and errors" - some had died, some had left the UK and some were now EU citizens.
BBC Home Affairs correspondent, Danny Shaw, said that Ms Homer had revealed the figures in a letter to the Home Affairs Committee Chairman, Keith Vaz.
Mr Reid had promised that the backlog would be cleared by 2011.
Ms Homer said she was "confident" this would happen because the process for checking the cases was being speeded up, with 900 caseworkers dedicated to the task.
She also revealed that a "very limited" number of foreign prisoners had not been considered for deportation before the end of their sentence.
Four cases had been identified so far - two individuals had eventually been detained, and two others had not yet been traced.