This was a trilogy about a future earth where double clones were made to fight wars and they nearly destroyed the earth. They were good fighters because they were mentally linked. All were supposedly destroyed but a few were found by this reporter type.
I believe the USA version were called Jeeks.
In the second book a space ship containing a bunch of them returned.
In the final book one clone of a command 3 person clone fought them (the other 2 in the triad were killed and somehow this one did not go insane).
I have looked for this book for 30 years.