Until now I was using rsync when I needed to limit bandwith, but on this morning I could read this on IRC :
<la_loOse> scp a aussi un -l pour limiter la bande passante
In english: scp has a -l option to limit bandwidth
And indeed, in the manpage:
-l limit Limits the used bandwidth, specified in Kbit/s.
I have no idea how old is this option...