You could ask the sausage machine (police Central Ticket Office) to show leniency due to the extenuating circumstances.
If that fails, for up to 86 in a 70 limit (10% +9mph), you should be offered a Speed Awareness Course (if caught in England & Wales) if you haven't done one for an offence committed in the 3 years previous to the current one.
Or an offer of a fixed penalty (for up to 95 in a 70) if you do not qualify for an SAC, or do not take one if offered.
Your circumstances do not constitute a defence for speeding, but might constitute Special Reasons Not to Endorse - mitigation relating to the commission of the offence, which is not a defence, but is sufficiently compelling to justify not endorsing your licence. This would be an argument you would run in court, having declined/refused any out of court settlement.
I would characterise SRNtE as a reason for comitting the offence that the bench themselves would admit to being likely to result in them doing the same. Personally, I would take the view that anyone who wouldn't exceed the speed limit to say goodbye to the dying mother on their death bed, assuming that it was safe to do so, had something wrong with them. That said, without knowing the road/traffic conditions, I would be minded to question whether you were urgently trying to get their as fast as was safe to do so, or whether you merely had more pressing things on your mind than the speed limit. N.B. The bench on the day might not see things as clearly as I do.
