Accountancy Age has reported that

The Translational Auditors Committee (TAC) of the Forum of Firms, a unit of the International Federation of Accountants (IFAC), has released a study which explores current practices among members of the Forum of Firms, an association of networks of international accounting firms that perform transnational audits.

The guidance paper, Tone at the Top and Audit Quality, based on the input of 10 TAC members, representing some of the biggest international networks, notes that, creating the right 'tone at the top' is not only an important element of corporate governance, but also key to effective operations of audit firms.

As IFAC put it:

Leaders of accounting firms have a responsibility to ensure that the commitment to quality is clearly embedded in their organisation's values, code of conduct, training, and reward policies.

Unless they quit the tax havens this objective is irreconcilable with the actions of these firms. You can't be committed to openness, accountability, honesty and integrity and work in those places.

The accounting firms have a choice.

But they can't have it both ways.