Welcome to Flyertalk, DWLondon, welcome to the BA Forum, and now that you have started to post, it would be even better if you could continue to do so. Welcome on board.

These fares, including those that involve the so-called "Saturday night rule", currently are totally inflexible - no refunds, no changes. I've just checked a dummy booking and that remains the current situation. One can imagine why, they are often below half the usual business fare. So if we are going to be allowed the £100 change fee that is indeed an attractive feature. Thank you for posting, I think you may have a scoop on that one.