What is the difference betwen a "messenger" and a "courier"

I dont come under the classification of one of the "children of Thatcher,"thank fuck.If I did I'd find that comment offensive and punchworthy.

I was making a point of the irony, not seeking to insult our package carrying bretheren.

Another irony often commented upon is that couriers, who are a manifestation of counter culture, make their living carrying the deeds and documents of the archdeacons of capitalist culture; bankers and lawyers.