Hi Frances, I realy do not have as much practice at training as many of the members you already have replies from.
What works with my pony Daniel varies, you said :
I clicked but she had an itch so started to scratch herself befor accepting the foodreward
well, sometimes Daniel will sidle over and place me alongside his tummy, then raise his hind leg, and if I am slow on the indulgent uptake, he points an extended muzzle to show me which spot to give circle scratches to. Usually this is his hoof and feathers, as well as the inside of the hind legs, hocks and ventral line of tummy. All the bits that are easier for me to reach than for him to attend to himself. He stretches that nose in ecstasy, so that is a reward.
But my horses also work for treats, carrots are a favourite, oats are worked hard for, and I do buy boxes of sugar puffs, honey coated puffed wheat, because they are light and easy to carry, and five puffs is less than half a grass nut.
Play and experiment with what works for you, have a look at these bonding tips:http://www.naturalhorsetraining.com/TrainingTips58.html
from Sylvia Scott naturalhorsetraining.com
Hope that is some help.