hi bathbun we also have an allotment alongside a beehive ,i realise you need to solve whats happening at yours it sounds weired,at first when we bagan to garden we were plagued by biteing horseflies and they really did hurt and the bites lasted sometimes over a week,however we were given Avon Skin so soft as this is what the marines use abroad for stinging insects and such and it works really well i also noticed the bees didnt come near us although they were not a problem anyway,you might want to try it and i know it sounds funny but almost everybody on our allotments use it in summer and swear by it,so it might not solve the problem of getting rid of them but at least you might be able to work untill its all sorted and its not expensive, good luck
Alan4711