I have just bought some new plants
I washed them ,checked for snails and planted them
two days later my fish dug one up and as i replanted it i noticed a small red worm about an inch long and the thickness of a piece of thread hiding in the roots it was very alive !!!!
Anyone got ideas as to what it might have been?

Sounds like a bloodworm to me, or may plantaria (sp.?). Neither of them are harmful, and will probably disappear within a day or so, most likely into the fish's mouth...

if it is a blood worm, would they reproduce in a tank?