70.This section applies to a person convicted of a scheduled offence committed during a period of remission for a previous conviction for which that person was sentenced to a custodial sentence of more than 1 year. In calculating the unexpired portion of a previous sentence it is important to note that time continues to run while a person is at large and so the actual effect of the section will depend on the time when the later offence is committed. This means that a person released on remission after serving say 2 years of a four year sentence who re-offended after the full term (4 years) of the sentence was expired will not be affected by the section, but a person who re-offended and was re-convicted after three years would be required to serve one year before starting his new sentence (the unexpired portion does not attract remission).
Commentary Part Vii: Northern Ireland Section 80: Conviction during remission