Umm. thanks for the alarmist title.. it's not an incest app.. it's an anti-incest app.

It's more of an anti-have-sex-with-distant-relatives app. Which doesn't count as incest, but is more likely to happen, since generally speaking, you don't need an app to tell you who your immediate family are that you might commit incest with.

Ever heard of this song?

Disagree.
You shouldn't be having sex with your cousin. ... even if they are 2-3 generations out.
But then again... you're in England.. so it may be a wee bit more permissible.

Read about this. Last name is no give away either, because Iceland still practices the old custom of your last name being your same gendered parents name with either -son or -dottir affixed to the end.

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Never heard that song but this one came to my mind:

Many, many years ago when I was twenty-three
I was married to a widow who was pretty as could be

This widow had a grown-up daughter who had hair of red
My father fell in love with her and soon they too were wed

This made my dad my son-in-law and really changed my life
For now my daughter was my mother, 'cause she was my father's wife

And to complicate the matter, even though it brought me joy
I soon became the father of a bouncing baby boy

My little baby then became a brother-in-law to dad
And so became my uncle, though it made me very sad

For if he were my uncle, then that also made him brother
Of the widow's grownup daughter, who was of course my step-mother

Father's wife then had a son who kept them on the run
And he became my grandchild, for he was my daughter's son

My wife is now my mother's mother and it makes me blue
Because although she is my wife, she's my grandmother too

Now if my wife is my grandmother, then I'm her grandchild
And every time I think of it, it nearly drives me wild

'Cause now I have become the strangest 'case you ever saw
As husband of my grandmother, I am my own grandpa

I'm my own grandpa, I'm my own grandpa
It sounds funny, I know but it really is so
I'm my own grandpa

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It's not such an absurd idea given the circumstance;
One of the world's oldest & smallest populations
growing up in virtual isolation.

Not only in England...but right here in the Ozarks....Brother/sister relationships are out...but 1st. cousins are fair game....

...not to mention long, cold nights
and limited cable TV & Internet...