You are SO lucky! I have grown this for years and apparently it normally needs both male and female plants, though there are self fertile varieties like 'Coolidge' available. This year mine was smothered with flowers on a four foot tree but not one of them set!
A couple of years ago we saw some well developed trees in the Gijon botanical gardens loaded with fruit that was almost ripe (in early November). We stole a couple of fruit and I have grown more bushes from the seed which I hope will pollinate my bought tree in a year or two.
But the fruit will only ripen very late in the season. Ideally as you are in the UK you should be growing this in a large pot so you can bring it into a conservatory or under cover to finish ripening. Alternatively, I would give it some cover like a fleece or even a polythene tent. The cooler the temperatures for ripening, the more 'off flavours' you get with the fruit. Feijoa or Acca is grown widely in the north island of New Zealand so ideally you need a warmer climate than the UK or even what we have here in France. Good luck though as the fruit is absolutely beautiful when ripe. Actually Torquay should be a good place for it with your maritime climate... can't be that much worse than north west Spain... so your chances of success as the tree develops should be good.

Hi Bertiefox

Thanks for answering.

Unfortunately I have nowhere under cover for plants of this size so I guess I will have to try fleece.

My plants are two of a number that I grew from seed (thompson and morgan). Only one flowered, the other does not and as far as I know the flowering one is not self fertile, I just get busy with an artists brush. I read somewhere that seeds can sometimes produce self fertile plants. It would seem to be a bit hit and miss, so good luck with your seeds and thanks again for your comments.