Are all these red fruits on one branch, and if so, where does the branch arise? At the base of the plant, or off the trunk, higher up?

Do you think the're from the rootstock Bamboo.I wondered?

The greenish apples in the first picture look remarkably like the ones which come from the dwarfing rootstock used for growing most Crab apples these days.

Thanks for ideas. They are from a branch off the trunk, I am a lover of gardens but a bit useless when something happens I don't expect.

I'm sorry, I typed red when I meant green - I meant to say, are the green fruits all on one branch, and does that arise from the base or off the trunk... Either way, you need to remove the offending branch. If its from the base, cut it out below the soil if you can, or wrench it off - you can do that now. If its off the trunk, then saw it off, but leave a little 'collar' of about quarter to half an inch, but don't leave a 'stub' sticking out. Support the branch as you cut it so it doesn't tear some material off the trunk - saw upwards from the underside first, then from the top down. The time to remove a branch from the trunk is really January or February, but I'm guessing, unless you mark the branch, it'll be difficult to tell which one it is by then.

If its coming from the roots, its off the rootstock - if its up the trunk, its just a bit of genetic reversion/misinformation.

Thank you Bamboo for that excellent advice, I am about to follow your instructions now.