His comments came as the Government this week told Cornwall Council it must do more work before the Local Plan can be approved.
The Local Plan, like Neighbourhood Plans being developed in towns and villages, aims to set out a vision for the growth and identity of the whole county in the future. It identifies the quantity of, and key sites for, new housing, community facilities, shops and employment.
The plan was submitted for examination in February and the Secretary of State-appointed inspector Simon Emerson was publishing his preliminary findings this week.
A spokesperson for Cornwall Council said: 'Mr Emerson has indicated that additional work is required from the council and possible changes need to be made to the plan to make it "sound" before it can be adopted.
'This is not unusual with over 60 per cent of plan examinations proceeding along these lines. Many others fail or are withdrawn to start again.
'The council will need to consider whether to agree to the further work as suggested and will do this over the coming weeks.'
Cllr Long (Mebyon Kernow), from Callington, says it is time for Cornwall to be in charge of deciding how many houses should be built here.
'I am disappointed but not surprised by the latest delay caused by the planning inspector. This is what we (Mebyon Kernow) warned would happen when we have a London- and Bristol-based organisation deciding on housing numbers for us in Cornwall.
'There is a popular misconception that the targets of 47,000 are upper levels.
'These are minimums – there is no upper limit. The National Planning Policy Framework (NPPF) is a developers charter. As such, it is encouraging mass house building across Cornwall and I fear that as long as we have London deciding these things, even our Cornwall Local Plan will not have the teeth needed to protect against over-development.'