send alarm bells ringing in the headquarters of the biggest US gun manufacturers. During the 10 years that Bill Clinton's ban was in place, the law was diluted by gun makers who made small cosmetic changes to the design of their weapons as a way of freeing them from federal controls.

The change might be as insignificant as moving a single screw in the firearm, but that was deemed sufficient to change the name of the weapon, remove it from the prohibition, and put it back on sale. Banned weapons were blatantly copied, with a minor design change, and again renamed and remarketed.

For instance, the Bushmaster XM15 that was deployed in Sandy Hook elementary school last month to kill 20 young children, six of their carers and the gunman'smother, was a copy conceived under the shadow of the Clinton assault rifle ban of the prohibited Colt AR-15.

Josh Horwitz, director of the Coalition to Stop Gun Violence, said it was crucial that the White House was aware of how the Clinton ban was undermined last time round and was determined not to let the same thing happen again. "This is very important. Unfortunately, the gun industry doesn't act in the spirit of the law – you have to hem them in effectively with watertight legal drafting."

An awareness of the tricks that gun manufacturers can play to sidestep the law has informed Senator Dianne Feinstein's bill on revising the federal ban on assault rifles that may form the template of the White House plans. She has modelled the