A tip from an old Scottish camper. They usually make for the light at night so if you need to go, leave a lantern or torch several yards away from you and your tent. If you get into a swarm you just cannot get rid of them. They go in your ears and mouth, fill your hair and up yer kilt. You mostly don't feel them bite but you will be full of itchy red spots next morning. I think the repelant they sell in tourist shops do the oposite and atract them. get one of these... 2 Lb Citronella Bucket Candles. They last ages and place it at the entrance to your tent. They smell nice and are safe but the midges hate it. I think you can get smaller ones but Citronella is the biz. I have no connection with this company, just googled. Many local shops in Scotland sell them.
http://www.gooutdoors.co.uk/none-2-l...ellent-p124609
Another tip. If they get in our caravan, we leave a few cups of water with a tiny drop of washing up liquid in each (to break the surface tension) around caravan and the light reflecting from the water attracts them, then they drown. May be a bit messy in a tent though.