One off or not....surely some of the point of having a VHF is to know what might be round the next bend....it's rare for a narrowboat to sink on a big river but you will be glad of a lifejacket when it does......"One off" events quite often happen before a serious accident. Taking simple and relatively cheap precautions such as a VHF, life jacket, anchor etc helps reduce the risk.
The attitude of some people on here who resent spending a small amount of money and a little time doing something like a VHF course really beggars belief. As has been said this mindset together with the lack of common sense that prevails today will see even more legislation and restrictions placed on us.
Cheers
Gareth