I got stitched up like that some years ago, in an insurance case. A vehicle behind ran into the back of me and produced a "witness" who was supposedly walking by. I exchanged details with the other driver and we both drove off together - they never spoke to anybody by the side of the road, and I certainly never saw anybody there,so where did the witness come from?
Didn't do me any good that they were lying in their teeth the pair of them.
The driver who went into me was a driving school instructor in a family business, so had a very heavy motivation not to be found in the wrong.
They even gave this supposedly independent and unbaised witness a lift to court and a �handshake" afterwards, laughing like drains. Sorry about the "�" there - that was a typo.
But one v two was not good enough....