Since you ask Richard. I think it's simply implicit at the moment.
I sit on a working party on behalf of the ICAEW. We are engaged on updating the Guide to professional conduct for those working in tax.
The working party also comprises representatives of CIOT, ICAS, ACCA, STEP, CIMA, ATT, IIT. Most of these bodies also collaborated in the creation of the current version of the Guide and I sat on the working party last time too.
The Guide is a de facto part of the ICAEW members' handbook and the update will reflect the creation of the merged HMRC, changes in the law and changes in practice. This is also the first time the Guide has had a thorough overhaul.
I've just had a quick scan of the current version and of the latest draft of the update. I will suggest to the working party that the point in question be made more explicit than seems currently to be the case.
1) Many thanks Mark
2) This shows the importance of blogging
3) I think this will pose real problems for many UK practitioners offshore
And, maybe a fourth:
4) If I could make a request the amendment would require that the members of those Institutes be required to make specific enquiry on this point and document their answers, with reasons and evidence given.