Rachel Reeves: 'I'll rip up rules on planning within days' - Labour's new Chancellor announces 'growth mission' which could see thousands of homes built on Green Belt land

Rachel Reeves will declare war on Britain's planning system today.

Vowing to take the 'difficult decisions' needed to boost economic growth, the new Chancellor will use her first major speech to reveal that the Government is beginning its assault on the planning rules.

Before MPs break for the summer at the end of the month, councils will be issued with mandatory targets to clear the way for hundreds of thousands of new homes. 

And ministers will begin work on controversial plans to weaken protections for some parts of the green belt to make room for development.

Ministers are also looking to relax planning rules for major infrastructure projects, such as the installation of hundreds of miles of new electricity pylons needed to link up wind and solar farms to the grid.

Ms Reeves will today declare that, with the public finances already stretched, boosting Britain's sluggish economic growth is the 'only route to improving the prosperity of our country'.

She will say last week's landslide election win gives Labour a 'mandate' for radical change – and will insist that planning reform is among the 'first steps' needed to 'fix the foundations of our economy, so we can rebuild Britain'.

'Our manifesto was clear: Sustained economic growth is the only route to improving the prosperity of our country and the living standards of working people,' she will say. 'Where governments have been unwilling to take the difficult decisions to deliver growth – or have waited too long to act – I will deliver.

'It is now a national mission. There is no time to waste.' Ms Reeves was appointed as Britain's first female Chancellor on Friday, and warned that there was 'not much money around'.

But union leaders, who have bankrolled Labour for decades, are already pushing her to open the spending taps.

Unite boss Sharon Graham said there was scope for the Government to borrow tens of billions of pounds to 'invest' in the economy and public services. 

She urged Ms Reeves to scrap Labour's tight fiscal rules and pour billions into Britain's 'crumbling public services'.

'We are going to have to borrow to invest,' she told the BBC's Sunday with Laura Kuenssberg. 'We have not got time to wait for growth.

'People are literally hurting out there and we are going to have to borrow to invest – our crumbling public services need money.'

Ms Graham's intervention is the first warning shot from the Left – and an early sign that the Labour leadership may find it hard to resist reverting to its tax-and-spend traditions. 

The union boss warned that new Prime Minister Sir Keir Starmer 'won't have a lot of honeymoon period' unless he delivers quickly.

Greater Manchester mayor Andy Burnham, on the same programme, called for a 'decisive break with austerity'. 

Sir Keir yesterday began a whistle-stop tour of the UK with a visit to Scotland, where he promised an 'immediate reset' of relations with the devolved administrations.

Tomorrow he will travel to the Nato summit in Washington where he will seek to reassure leaders that his Government can be trusted on defence despite ditching Rishi Sunak's pledge to raise military spending to 2.5 per cent of GDP by the end of the decade. 

Labour's decision to target the planning system immediately is likely to bring it into conflict with both countryside campaigners and those communities that feel they are already at the limit of development their area can take.

It could also trigger a backlash from some of its own MPs who represent a swathe of constituencies across southern England where planning reform has been resisted for years.

During the election campaign, one Labour official said the party was prepared to 'flatten the whole green belt'. This was denied by Labour.

Ben Houchen, Tory mayor of Tees Valley, said promising rapid growth on the back of planning reform could become 'a noose around the Labour Party's neck'. 

He added: 'How keen are the Labour Government to tinker with environmental regulations which is one of the largest delays in the planning system?'