The tag on SVN has a space in it, but the tag in git had this space converted to %20
(URL encoded). To solve it just manually add a new tag with the verbatim name:
cd .git/refs/remotes/tags/
mv Sync%20Controllers Sync\ Controllers
Then run the git svn clone
command again.
(Normally you’d do this with git tag OLDTAG NEWTAG
but git was not allowing me to define a tag with a space in. The tag files are simply text files containing the hash of the relevant commit.)