At all the pools I've been to in the last few years, there is a real etiquette especially for lane swimming.
Signs at the end of each lane, indicating fast or slow lane, and whether to swim clockwise or anti clockwise.
If you go in the fast lane, it's pretty much front crawl only.
Over taking is done down the middle, and if you're going to overtake someone, you have to do it quickly, and then move back to the outside of the lane.
It is like the tour de commute, you're not really racing but you are racing, if you're in the fast lane, you're not going to wait behind someone slower. However, if you're going to overtake someone, you've got to stay ahead of them for a reasonable number of lengths before stopping for a breather.
People who go to the fast lane when it's empty to slowly swim up and down doing breast stroke should return to the slower lanes when someone fast enters the lane.
The unwritten etiquette of the pool is as immutable as the written rules (no running, no bombing, no petting, no cut off jeans)