Hmmm... asking about distance from the kerb is asking the wrong question, surely.
According to Cyclecraft (p 85-92), the standard riding positions away from junctions are:
The primary riding position - in the centre of the leftmost moving traffic lane for the direction in which you wish to travel
and
The secondary riding position - about 1 metre (3 feet) to the left of the moving traffic lane if the road is wide, but not closer than 0.5 metre (1.5 feet) to the edge of any road
It goes on to say on p 88: "Follow the traffic, not the edge of the road - The secondary riding position is always relative to the moving traffic lane, not the road edge. Riding further left, even if there is space, will reduce your ability to be seen by other drivers and the notice they will take of you."
"Only on long stretches of road where there are no side roads, drives or other entrances and you are travelling very slowly (perhaps up a hill) should you allow yourself to ride further to the left than the secondary riding position, but always keep at least 0.5 metre (1.5 feet) from the edge. Conversely, if you are travelling quickly, keep further out."
More on Primary riding position:
"The primary riding position should be your normal riding position when you can keep up with traffic, when you need to emphasise your presence to traffic ahead, or when you need to prevent following drivers from passing you unsafely." (p. 88)
On p 90 John Franklin states that an important exception to the rules for holding the primary riding position is when there is a significantly increased risk of being hit from behind, owing to bad visibility (fog, heavy mist, fine persistent rain); caution is also needed at pub closing time. ".... At each of these times, it is prudent to keep further left and to take special care near junctions. You may also find it difficult to move to or maintain the primary riding position along narrow main roads where traffic is fast and continuous. Your only option here is to ride as best you can and reduce speed at hazards if you cannot move out. At all times, make sure you have good control of your bike by grasping the handlebar firmly, but you may get more clearance from traffic if you do not steer too straight a course." (p 91).