Cornwall and the Isles of Scilly is on track to miss the Government's housebuilding target by thousands of homes, new figures suggest.

An urban policy think tank said England is in a "productivity crisis", and urged the Government to be "much more ambitious" to achieve its 1.5 million housebuilding target over the next five years.

It comes a few weeks after the Government announced changes to the National Planning Policy Framework aimed at achieving sustainable growth in the planning system to reach this target.

But Centre for Cities figures estimate the Government would still fall 390,000 homes short, even if private development across the country rose to the same level as its strongest ever period of performance under the current planning system.

Based on historical analysis of housebuilding since the postwar reconstruction period, the think tank's figures suggest the Government’s proposals may deliver up to 1.1 million new homes by 2029 through the private sector, with the remainder unlikely to be bridged by the public sector.

In Cornwall and the Isles of Scilly, the analysis estimates 3,282 houses will be built each year until 2029, which is below the 4,454 local target set by the Government.

By the end of the four-year period, housebuilding in the area will have fallen short of its total target by 4,688 homes.

Andrew Carter, chief executive of Centre for Cities, said the Government must be "much more ambitious" for England to reach the "bold housing target" it has set.

He added: "We’re in a productivity crisis. The UK’s big cities are the jobs and productivity engines of the economy but our planning system doesn’t allow – and has never allowed – them to build an adequate supply of homes for everyone that could work there."

Centre for Cities argues the Government has failed to address the constraints placed on housebuilding by the discretionary planning system in cities and the green belt — which it says is explicitly established to block suburban development.

Mr Carter added: "By removing the discretionary element of the planning system, the UK would bring its planning system in line with most developed economies, remove a big block on housebuilding and enable places to better respond to future rises in demand for homes.

"We have done wholesale planning reform before and we can do it again.

"What we can’t do is raise national economic growth – and reduce the strain high housing costs place on people’s spending power – if we don’t address the backlog of missing homes."

Centre for Cities figures predict under-delivery of new housing following the latest planning reforms will be largest in big cities.

Over the next four years, private development may fall short by 196,000 new homes in Greater London — 60% under the area’s target — and 96,000 below objective in all other big cities.

A Ministry of Housing, Communities and Local Government spokesperson said: "Despite the dire housebuilding inheritance we are trying to fix, we will deliver the 1.5 million homes our country desperately needs and get Britain building again.

"To get there the Government has already outlined plans to streamline the planning system, restored mandatory housing targets, established a programme to unblock homes stuck in the planning process, and set up a new body to deliver the next generation of new towns.

"On top of this our Planning and Infrastructure Bill will go even further in overhauling the planning system to boost housebuilding and economic growth across the country."