Thank you all for your suggestions and help.

I've achieved results good enough for my purpose which is 3D printing.

I choose a 12 tooth pinion and a 30 tooth gear using Module 2 meeting at 90 degrees.

I used the formulae from the info that Brian supplied to calculate angles - see below


Basically I trimmed one gear profile from the spur gear script output, extruded it to a point, laid it down on a cone and arrayed the extruded profile around the cone.

I think that it's a bit of a bodge because I couldn't find a way to extrude to the point that I wanted to extrude to which was vertically above the pitch circle I could only extrude to a point vertically above the centre of the bounding box - auto chosen (as far as I could tell) by the extrude-to-a-point function. This introduced a very slight error that I had to fudge my way around.

Images below and file attached.

Mike.