Front anti roll bar diameters

Thank you I very much appreciate your help in confirming that.

You are very welcome! 
Everyone here wants you to resolve it.

I might grumble about my car but I love it and come time I will have it sorted. I'm in it for the long haul and I learn from every post.

If it’s any help, the standard blue flash front springs I removed have a free length of 247 mm. Roger Parker’s book states 2002 spec roll bar at 18mm and 2005 spec at 20mm, however this does not tally with my 2002 car which is 20mm.

I concur.
My 2002 is absolutely 20mm.
It's almost factory new with no blistering or flaking and the coating is not 2mm deep!
A bit of anomoly.

Now you understand the reasons for asking for detail in the responses.
We need some owners with 2005 cars, comfort pack cars, and the 85 to do us a favour and measure their anti roll bars.
Ideally report some other details too but that would be too demanding.

The value offered for free length is also interesting as most sources have 242 or possibly 244, the WSM I have suggests 242.
The additional length offered by the 247 recorded above would make the ride height that much greater by 5mm.

There was clearly a degree of latitude in the intended ride height or “trim height” as the WSM refers to it.
Standard front is quoted as 358 + or - 10 mm
Sports 348 + or - 10 mm.