> Wouldn't it be better for str(um_ver) to generate 1.02 instead? Or is there a very good reason for this not to be the case ...

See notes below : https://github.com/SciTools/iris/pull/1141#issuecomment-45223337
From notes there.. it seems that the "1.02" approach is just "wrong".

**My aim here** is simply to replicate the existing ("wrong") rules behaviour
 -- so that is why it doesn't use ```str(um_ver)```.

Following another decision from @marqh, we are shortly also going to remove the version from the 'source' string anyway -- see https://github.com/SciTools/iris/pull/1142