After 20 years of visiting the West Coast and Highlands (at least twice a year most years) I can confirm that the only thing that works against midges and is user friendly is the Avon Skin So Soft but make sure you get the correct type.
Avon sell a wide range of products under the "Skin So Soft" label but the one that contains the citronella that deals with the midges is Avon SSS Replenishing Dry Oil Body Spray. It's very easy to get hold of in Scotland in outdoor shops or newsagents/grocers or on campsites.
Avon don't give any information on this because if they sold it as an insect repellent it would have to be licensed as a pharmaceutical.