Section 187 applies in relation to a person if the conditions in subsections (2) to (6) are satisfied.
The first condition is that the person was extradited to a territory in accordance with Part 1 or Part 2.
The second condition is that the person was serving a sentence of imprisonment or another form of detention in the United Kingdom (the UK sentence) before he was extradited.
The third condition is that—
if the person was extradited in accordance with Part 1, the Part 1 warrant in pursuance of which he was extradited contained a statement that it was issued with a view to his extradition for the purpose of being prosecuted for an offence;
if the person was extradited in accordance with Part 2, the request in pursuance of which the person was extradited contained a statement that the person was accused of the commission of an offence.
The fourth condition is that a certificate issued by a judicial authority of the territory shows that—
a sentence of imprisonment or another form of detention for a term of 4 months or a greater punishment (the overseas sentence) was imposed on the person in the territory;
the overseas sentence was imposed on him in respect of—
the offence specified in the warrant or request, or
any other offence committed before his extradition in respect of which he was permitted to be dealt with in the territory.
The fifth condition is that before serving the overseas sentence the person was returned to the United Kingdom to serve the remainder of the UK sentence.