Ministers have no idea what impact the money has had, they warned.
The scale of serious drug addicts has remained stable at around 330,000 since 2004 and they cost society around £15 billion a year, virtually all of which is related to crime.
The Commons Public Accounts Committee said the Government spends £1.2 billion a year tackling problem drug use but does not know how effective measures are.
The MPs also called for more drug addicts to be met at the prison gates to ensure their rehabilitation continues outside jail and signalled the worst addicts may be better dealt with in secure residential...
