US politicians are drawing up a bill that could make it less attractive for Wall Street investment banks and other financiers to repackage risky mortgages into securities and then sell them to investors around the world.

In particular, senior figures in Congress hope to force the financiers who buy mortgages and create mortgage-backed securities to share some of the liability - and thus financial cost - that might arise if mortgages were mis-sold to borrowers who proved unable to meet payments.