* test
This does not work:
#+call: year2016[:cmdline --format "%-20A %12T\n" bal --flat pay tax]()

#+results:

This one does:
#+call: year2016[:cmdline --format "%-20A %12T\\n" bal --flat pay tax]()

#+results:
: pay                      -35.00 £
: tax                       10.00 £
:                          -25.00 £

#+name: year2016
#+begin_src ledger :cmdline bal assets
  2016/05/03 * pay
      bank                                       25.00 £
      tax                                           10 £
      pay
#+end_src