Hi, welcome to GoY, your polytunnel was probably just too cold for them, the optimum growing temperature for aubergine, [Solanum melongena], is 70 to 85f, and if the temp drops below 60f, eg overnight, fruit set is reduced, they prefer a fertile, humous rich soil, with a ph of 5.5 - 6.5, they also resent root disturbance, they're 1 of those 'fussy' tropical plants, tomato's are a bit less fussy, but still like decent temperatures, but not quite as high as aubergines, Derek.

If you were growing them in a polytunnel, the most likely explanation for no fruit setting (assuming they were not short of water) was no pollination for the flowers - these are wind pollinated, and in a polytunnel, that's not really something that can happen. They are self fertile, and each flower has male and female parts, so you could try just giving the plants a gentle shake as often as possible once the flowers are present to encourage pollen to fall within the flower. Otherwise, a clean paint brush moved around inside the flower (gently, so as not to break anything) should do the trick. Some people use battery operated electric toothbrushes - you place the toothbrush on the vine, near a fully open flower, and switch it on.The vibration is usually enough to cause the pollen to drop to the right place. Course, if you're growing a lot of plants, hand pollination can be pretty time consuming.