I have been using Blender for about 3 months and gained a reasonable skill level with it.

One thing I am not clear about is the co-ordinates. When you start you have the y in vertical direction and x horizontal. Fine.

When pressing ctl and 0 to get camera view the x, y plane is lying horizontally with z pointing upwards. So either camera is rotated or model by 90 degrees to view properly.

Okay, I am fine with that. ctl-0 and 0 both give camera view.

Still not understanding why :

camera defaults to being upright in z direction rather than upright in y direction.

ground grid is being drawn in x-y plane.

This situation is the same on both my installation at home and also in work so it is not an issue with the installation being corrupt but some feature I am not getting!!!

It is the convention blender uses – x,y is the ground and z is the elevation. This is also the convention most engineering software uses x and y are the easting and northing with z being the elevation.

Blender has the mathematically correct way of doing things - its just the other 3d software I have used chooses different (Poser/DAZ Studio).

From Wiki -->

Once the x- and y-axes are specified, they determine the line along which the z-axis should lie, but there are two possible directions on this line. The two possible coordinate systems which result are called ‘right-handed’ and ‘left-handed’. The standard orientation, where the xy-plane is horizontal and the z-axis points up (and the x- and the y-axis form a positively oriented two-dimensional coordinate system in the xy-plane if observed from above the xy-plane) is called right-handed or positive.