1. The question whether the appellant “is a persistent offender” is a question of mixed fact and law and falls to be determined by the Tribunal as at the date of the hearing before it.
2. The phrase “persistent offender” in s.117D(2)(c) of the 2002 Act must mean the same thing as “persistent offender” in paragraph 398(c) of the Immigration Rules.
3. A “persistent offender” is someone who keeps on breaking the law. That does not mean, however, that he has to keep on offending until the date of the relevant decision or that the continuity of the offending cannot be broken. A “persistent offender” is not a permanent status that can never be lost once it is acquired, but an individual can be regarded as a “persistent offender” for the purpose of the Rules and the 2002 Act even though he may not have offended for some time. The question whether he fits that description will depend on the overall picture and pattern of his offending over his entire offending history up to that date. Each case will turn on its own facts.
Seems sensible enough.
Source: Chege (“is a persistent offender”)  UKUT 187 (IAC)