The Government does not set targets for housebuilding. It is for local authorities to identify their housing targets, in light of national policy and guidance. In the case of Milton Keynes, this is set out in their current local plan (adopted in March 2019).
The Housing Delivery Test, measures local authority performance against these locally set targets. Local authorities are rising to the challenge, and the Government publishes these results annually. The 2019 measurement shows that nearly two thirds of authorities have delivered the numbers of homes their communities need.