If an IPP sentence is given, the length of that sentence is indeterminate. However, like a life sentence, the judge sets a 'tariff' which determines when the offender might be released. Given the number of previous convictions, the judge might decide upon an IPP sentence, with a tariff of, say, 5 years. That would mean that the offender would remain in prison for at least 5 years, after which he would only be eligible for release if the authorities believed that he no longer presented a risk to society.
Prison reform groups have recently been campaigning for the increased availability of suitable courses in prisons, for people given IPP sentences. As things stand, such prisoners can't be considered for release until they've satisfactorily completed the relevant courses, but many prisoners find that the courses aren't available to them. This means that many people sentenced to IPPs stand no chance of getting out of prison until many years until after their tariff ends, if at all.
Chris