What are the advantages and disadvantages of a politically appointed vs. permanent Civil Service?

The United Kingdom¹ has a permanent, and (in theory, at least) politically neutral Civil Service - although it is sometimes argued that this neutrality has been eroded in recent decades.

In contrast, in many other countries appointments to the Civil Service are explicitly political, resulting in repeated, widespread changes to the make-up of the state bureaucracy on each change of government.

What arguments can be made in favour of, or against, these two models?

¹ I don't mean to suggest that the UK is unique in this regard - it just happens to be the country with this model that I'm most familiar with.