I was cycling home from work in Manchester, and I was cycling close to the edge of the road, as the OP would want me to - when a bus went past me so close that I had to swerve, so it didn't hit me.
It is just sheer luck that I was by a section of dropped kerb, and was able to mount the pavement. If I had been by a normal section of kerb, I would have hit it, fallen off, and might have ended up under the wheels of the bus.
THIS is why it is not safe to cycle close to the edge of the road - as other posters have said, it encourages drivers to try to squeeze past when there is not enough space for them to leave the cyclist a safe space around them, and when a driver passes too close to a cyclist, it is the cyclist who is at great risk, not the driver.
If I had been riding further out in the road, the bus driver would have had to wait until it was safe for him to pass me, and I would not have been out at such risk.
If a cyclist is clipped by a car's wing mirror and falls off in busy traffic, will the cars around them have enough time to swerve and miss them? Not always. This is why drivers should leave adequate space when they pass a cyclist - but far too many don't, forcing cyclists to cycle further out into the road to ensure their own safety.
Also, the road quality at the edge of the road can be really bad - pot holes, broken glass etc, etc, all of which are hazards to the cyclists, and it is safer for them to cycle a bit further out than to have to swerve suddenly to avoid one of these hazards.