for me, i think it should mainly depend on who the victims of the crime or injustice... i mean, if the "victim" is a national of UK, then the "criminal" should be tried and serve sentence in the UK...

if i remember it right, a US soldier was convicted of rape in the Philippines... he was imprisoned in the Philippines for a few weeks and later on deported to US to serve his remaining jail term... not sure if he's still in though...