So when is discretion not discretion? When it is "Industrial". Is that what you are saying BOAC? Surely not!
CAP 371 is quite clear and makes the presumption in favour of limiting the duty to the permitted FDP. It is the exercise of discretion to extend a duty which requires justification possibly, not the lack of will to extend beyond permitted FDP. In my submission no justification is required and a Commander is entirely within his rights to refuse to "go into discretion" (which is a misleading phrase anyway) without assigning any reason whatsoever.
There can be no such distinction as between an "Industrial" reason or indeed any other for failing to agree to extend a duty period.
In the particular case the subject Commander is a well respected individual who has a number of issues with the company. Having elected to accept a 75% roster (A few months ago when CX was shedding pilots!) she found herself in a situation where she had almost as much FDP as a 100% roster due to some highly creative work by crewing. She was being rostered to the limit virtually every day. When she complained it is alleged that she was treated inappropriately and subsequently has been discriminated against on a number of grounds. This treatment is and was the subject of formal complaint which may or may not lead to Legal proceedings.
Against this background she found herself in a situation where a duty would extend beyond prescribed FDP, warned the company that she would not be prepared to extend before the duty (which they did not heed) and, surprise, surprise, when down the line FDP was to run out, packed her bags and went to a hotel for the night.
So BOAC, by your estimation, you would say this was an "Industrial" refusal. Here is someone who alleges that she is being abused by the Company on a number of fronts, with zero tolerance and goodwill as a result. The response of the manager concerned is of no surprise to those of us who are familiar with him. I suspect he will come to regret it.
What is needed is a clear statement either from the CAA or a judicial interpretation of what otherwise seems quite clear in plain english. Otherwise it appears that the word "discretion" will have been hijacked by inept management who, having lost the good will of their workforce, are seeking to beat yet more work out of an already tired and demoralised community.