I've rode bikes for transportation in the US for over a decade now, and I can't agree. My average speed is around 12 mph. That's a bit faster than what you say your speed is in another comment. But it's still much slower than typical motorized vehicle speeds. I don't need to keep up with traffic, just make sure that they drive safely around me.
> Or if you are going uphill and you are concious you arr holding up all trafic
That's not your problem. In most jurisdictions (in the US, at least), the roads are first come, first served. Don't slow people down more than necessary, of course, but don't worry about it if it's unavoidable. I personally avoid these situations by taking longer routes that have less traffic, and not riding when traffic is heavy or waiting if there's a temporary increase in traffic.
> If you are going slowly on narrow UK road you get overtaken by double-decker bus with 2 inches of clearence. It's a harrowing experience.
If the lane's not wide enough to share, don't share. Taking the lane as appropriate has greatly improved my safety on the road. I usually ride to the right, but I'll take the lane when necessary for my safety and refuse to apologize for it.