- North Korea is a very poor country.
- Nuclear programmes are extremely expensive.
- North Korea menaces its neighbours to extort concessions to alleviate their poverty without reforming their economic system.
- They aren't particularly bothered by international condemnation.
- The concessions that they believe they will receive must be greater than the cost of a nuclear programme.
- Therefore refusing to make any concessions or enter any negotiations with North Korea would hasten their collapse.
* I say 'we' but the UK doesn't matter that much in that part of the world, it is the USA, Japan, South Korea, China & Russia who matter.
Update: Of course I should bear in mind that there is a possibility that they are as insane as they appear, take this for example:
May 24, 2009: It has been revealed that Choe Sung Chol, who was in charge of North Korean relations with South Korea, was fired and executed last year. The new South Korean government has reversed a policy of giving North Korea lots of goodies with no strings attached. South Korea now wants North Korea to halt developing ballistic missiles and nuclear weapons. North Korea takes this as a hostile act and an attempt to overthrow the communist police state in North Korea. Choe Sung Chol was apparently held personally responsible for the new South Korean government coming to power, and killed for this failure.
Imagine if we shot David Miliband everytime a foreign country adopted policies we opposed.