Susan was no more than puzzled when she saw the first results from her home DNA testing kit.

Now a woman in her mid 70s, she had never known much about her grandfather, and paid for the private test to see if it threw up anything unusual.

"I did notice there was a lot of Irish heritage, which as far as I knew was wrong," she says.

"But I just pushed it aside and didn't think any more of it. I stopped paying for my subscription and that was that."

Except it very much wasn't.

It took another six years for Susan - not her real name - to realise everything she knew about her family history was wrong.

She later found out that back in the 1950s, she had been swapped at birth for another baby girl in a busy NHS maternity ward.

Her case is now the second of its type uncovered by the BBC. Lawyers say they expect more to come forward driven by the boom in cheap genetic testing and ancestry websites.

A sharp, funny woman with shoulder-length white hair, Susan tells me her story from her sunny front room somewhere in southern England.

Her husband is sitting next to her, jogging her memory and chipping in from time to time.

After taking that DNA test almost a decade ago, the genealogy company entered her data into its vast family tree, allowing other users to make contact with their genetic relatives – close or distant.

Six years later she received a message out of the blue.

The stranger said that his data matched hers in a way that could only mean one thing: he must be her genetic sibling.

"That was just panic. It was every emotion I could think of, my brain was all over the place," she says.

Susan's first reaction was that she may have been secretly adopted. Both her parents had died some years before, so she plucked up........

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