But Mr Vine's report said the unit quickly became overwhelmed and failed to routinely or consistently make security checks to try to trace some of the unresolvedcases subsequently archived.
Mr Sedgwick told MPs that the agency had always tried to give MPs accurate information on unresolvedcases but there was a "necessary imprecision" about the figures because of the number of years over which they had accumulated.
Mr Vine said the agency had failed to routinely or consistently make security checks to try to trace some of the unresolvedcases that had been subsequently placed in the "controlled archive", a list of people UKBA officials believed they could not trace.
One key unresolved question revolves around how many of the remaining cases against Merck involve plaintiffs who only took Vioxx for a relatively short period of time.