'When to divert' is when you can no longer achieve CMR at touchdown - or earlier, of course. The former easily proven if the suits have go at you - from your PLOG.
Out of interest I spent my last almost 5 years after BA as what is now known as a 'zero-hour' pilot (then an 'ad hoc') with a small airline with the same 'insecurity', and not once was my fuel uplift ever questioned, be it PLOG or extra, and not once did I wish I had more. I think that without exception careful routing and level choices actually 'made' fuel en-route too. I accept I came into it with a background of experience, but from what we read, RY does not actually appear to be quite so draconian as some suggest. It could even be that those at the 'bottom' were extravagant and need 'educating'? Who knows - they probably do.
1066 - yes, 2000-2001 I think. I actually told one suit I didn't give a fig where I was and invited him to 'insert' the book.