Impartiality at the BBC: what constitutes a personal opinion?

The Impartiality & Diversity of Opinion section of the BBC Editorial Guidelines addresses at length how the BBC perceives impartiality and how it aims to make sure it is implemented across all of its programming.
The introduction states:
'Impartiality lies at the heart of the BBC's commitment to its audiences. It applies across all of our services and output, whatever the format, from radio news bulletins via our web sites to our commercial magazines and includes a commitment to reflecting a diversity of opinion.'
At the same time, a commitment is made in the ‘Personal view, authored programmes & websites’ subsection to allow, ‘a wide range of individuals, groups or organisations to offer a personal view or opinion, express a belief, or advance a contentious argument in our programmes or on our websites.’
But what of BBC journalists? Are they allowed to give their opinion or is this right reserved for guests? The answer is not entirely clear and herein lies part of the problem.
The relevant paragraph reads:
'Personal views can range from the outright expression of highly partial views by a campaigner, to the authored view of a specialist or professional including an academic, scientist, or BBC correspondent, to those expressed through contributions from our audiences.'
It is unclear, however, what the difference is between ‘highly partial views by a campaigner’ and ‘the authored view’ of a BBC correspondent. Does an ‘authored view’ constitute an opinion? If so, then this breaches a core principle outlined in the introduction:
'[O}ur journalists and presenters, including those in news and current affairs, may provide professional judgments but may not express personal opinions on matters of public policy or political or industrial controversy. Our audiences should not be able to tell from BBC programmes or other BBC output the personal views of our journalists and presenters on such matters.'
Even this principle is not without its problems. What is it about a ‘professional judgment’ that distinguishes it from an opinion? The BBC itself seems unclear. For instance, in the recent case against Jeremy Bowen, where an accusation of impartiality was partially upheld, the defence put forward by BBC News was that Bowen had been ‘exercising his professional judgment.’
It seems that there is a lack of clarity about what BBC reporters are and are not permitted to contribute when it comes to issues of controversy. On one hand, the corporation is adamant that the audience should not be able to tell what the personal views of its journalists are, but on the other hand, terms like ‘professional judgment’ and ‘authored view’ seem to provide reporters with the tools to bypass this commitment.