They sell pawpaw in the UK. I was very tempted to buy some actually! (Ebay)
However you need male and female tree to cross pollinate and it is unlikely that neighbours will have one, as its very possible with apples or pears.
In the UK you can grow a lot of variety of plants. However simple growing is not the same as fruiting.
UK summers are just not long enough (even more sunny East and south of England), too cool, and not enough sunshine for many species of fruit trees to ripen.
You can grow beautiful varieties of pomegranate - but the flowers will almost never turn into fruit.
Thisnis the reason we mostly grow tomatoes in greenhouses/polytunnels. When grown outside, usually as soon as they start turning red, the weather turns too cold 🥶
In Sweden or Norway, further north than Shetland you can grow more variety of fruit and veg outside - more sunshine in the summer.
We don't get summer - we get super long spring and autumn with couple "heatwaves" between May and August.
I have seen 24C (around 74F?) in April and next week frost!