The objective of the PIP scheme was originally stated in Parliament as being to save £1.5 billion per year. For example in 2013 the House of Commons Library reported, "PIP was originally expected to reduce working-age DLA caseloads and expenditure by 20 per cent, giving savings of around £1.5 billion a year by 2016-17".
So I asked the Treasury how this was being monitored because the key is the net savings figure. I.e. the cost of the payments to Atos and Capita for doing the assessments and any bonuses paid to officials involved in delivering the scheme etc must be deducted to establish the correct figure.
You can see here that there is no monitoring of the real costs or savings of PIP. Astonishingly MPs, and everyone else, have no means of assessing whether the policy intention of PIP is actually being delivered. That is because the real purpose of PIP was not the one stated. In fact it is a scheme to take money off disabled people and give it to people who already have a lot of money, namely Atos, Capita and other over-priviledged people involved in the scheme.