Thanks for all replies.
I'll try to train harder and recreate the race terrain etc more closely, race more (I don't do many races and I find it difficult to push hard in training) and salt / high5 load a few days prior to the race.
It feels odd to actively add salt to things as it is generally something I try, without success, to reduce. I guess the thing is to minimise it as much as possible normally and then load up a few days leading up to the race.
Iain, I can't imagine eating more bananas than I do already, but maybe I could find something similar to go with the bananas? - avocado, butternut squash......