The majority of steel concrete reinforcements in this country are made from 100% recycled steel. Reinforcements suppliers should be able to tell you where they source their steel from. Using recycled steel requires less energy that smelting virgin iron-ore, and so reduces the embodied CO2 of the build.
Click to open the following link in a new window (see above):
http://www.greenspec.co.uk/greening-of-concrete.php