git-svn, merging et al.

Ok - it's Friday and I've got to interact with svn again..

I'm using git-svn, and I've not followed the guidance. Development has gone on in git branches and merges - but now I need to commit the changes back into svn, and dcommit is, understandably, not very happy.

I'm intending to instead do something like a
  git format-patch svn-branch..git-branch
  git checkout svn-branch
... apply all the patches ...
  git commit
  git svn dcommit
  # back to the git work
  git checkout git-branch
  # this shouldn't have to do merging - but it will have the parents
to make it clear where the last merge happened from ?
  git merge svn-branch

I'm happy that I'm bludgeoning changes in one big blob into SVN, as I can reasonably say 'if you want the real details, go look at gitweb)

I've tried doing this with
 git checkout svn-branch
 git merge --squash git-branch

But I don't get the result I'm expecting - what have I missed?