Is this fruit edible, please?

They re definitely not conkers

They are generally tropical but I'm not sure if rambutans or longans could be grown here more successfully?

Horse chestnut leaf.....

Durians look similar, with a spikey outer skin but you'd know about it as the smell would strip paint

Sweet chestnut tree leaf.........

If all else fails oldgoat, you can upload a photograph of it onto the Woodland Trust "Identify this Tree" app. It's free of charge. And then come back and tell us!

Beech nuts?

According to my plant identifier it’s a Black Walnut

Bingo! Well done BlueBelle!

Pickled walnuts, mmm.

I don’t think I have had a fresh walnut!

Very very different to a supermarket walnut. Enjoy!

Don't eat unless you're absolutely sure, oldgoat!

Now, we have a lovely crop of small mushrooms around our tree .....

Double check , our Walnuts all have bright green husks not brown.

BlueBelle

According to my plant identifier it’s a Black Walnut

Leaves are completely wrong. Have a look at the close ups on this page full of images

duckduckgo.com/?q=black+walnut+tree&t=chromentp&iax=images&ia=images&iai=https%3A%2F%2Fwww.farmanddairy.com%2Fwp-content%2Fuploads%2F2014%2F09%2FDickieBirdFarm-BlackWalnuts.jpg

Not beechnuts, much smaller, woody, case

Not sweet chestnuts, case is covered with hairlike bristles

Not horse chestnut, case is green

Still agog to know just what it is

I’m sure it is of the Aesculus genus, or chestnuts. Possibly Aesculus indica, or Indian Horse Chestnut.

Mum used to make both quince and medlar jellies. Where on earth would these have come from in the 50's ? This thread has reminded me.

How big are the fruits, OldGoat?

It looks a bit like the strawberry tree but I don't think the leaves are right.

Sorry that I haven't come back with the answers to your questions yet.
I am suffering from a Zoom Conference bad back! I had a lovely long chat , via zoom, with some GNs that I usually meet in the flesh. At the end of the chat I tried to stand up and found that my back had gone into painful spasms. So beware Zoom. It could be bad for your health.

I'm off to try and get one of the fruit right now, suitably dosed up with paracetamol and Tiger Balm.

I may be gone some time!

I don't think it's a black walnut. We have one in our garden. The leaves are very different and the fruits have a smooth green outer case. They tend to go a bit browner and wrinkly once they fall from the tree.
If you gently rub the leaves of a black walnut it will release a delicate citrus fragrance.

https://www.gransnet.com/uploads/talk/202008/medium-839401-20200827-132617.jpg https://www.gransnet.com/uploads/talk/202008/medium-277443-20200827-132257.jpg

Here is a close-up of the mystery fruit. I'm sure it's some sort of walnut.
I rubbed the leaves fiorentina but couldn't smell a citrus smell.

Thanks everyone for your help. The fruit is obviously far from ripe though.

lychee?