Hi Anke - you're forgiven, I might have drained your brain regarding willow-herbs.
Anyway, if you follow the link on my original post, this is what Scottish Government says..
a bolus and an ear or pastern tag (the tag must be black) with the same unique 12-digit number
this is under the subheading of
Double identified: two non-electronic identifiers
which ain't totally right, but close....
There's some discussion about using a bolus in sheep, and they agree that owners won't need readers. The only thing they were worried about was carcass condemnation, but for me that sounds like small fry.
Any yes, I can see the appeal of not bothering with the bolus (still not sure about plural...)
Christian