I ordered posters from one seller in the uk, then from another seller a week later in the uk. The second purchase arrived in 2 weeks. The first purchase, ordered before the second and shipped before the second, arrived 6 weeks later. Go figure. The Royal Mail sucks.
The only thing worse, now, is the privatized mail in the Netherlands. I sent some stuff to someone there recently, and they lied about receiving it, claiming the wrong address was used, then lied about returning it though they never did, and they kept kicking the tube back to customs again and again. After about 2 months or so, the poster tube was finally delivered. They were the worst ever.