Smokers in a north-east London borough will not be able to foster children from January 2010 - unless there are "exceptional circumstances".
If a child is in care then that is a pretty exceptional circumstance all by itself. If there were a surplus of foster carers then the policy might be justified as a way of filtering the candidates, but according to everything I have heard there is in fact a shortage. The justification for the ban is that most evidence suggests that various risk factors correlate with being in a smoking environment and this is true. However there are also strong correlations between poor life outcomes and being in care. and it seems implausible that children raised in households with smokers do worse than those raised in care homes. So the reasoning behind the ban demonstrates an inability to quantify risk.