Labour leader Sir Keir Starmer has vowed to introduce legislation that would allow the Office for Budget Responsibility (OBR) to independently publish its own impact assessment of any major and permanent tax and spending changes.

His shadow chancellor, Rachel Reeves, said it meant that "never again" can the "disastrous mistakes" of the former prime minister be repeated, ahead of the first anniversary of her "fiscal event".

Tories accuse Starmer of wanting to 'return to agonies of the past' - politics latest

The mini-budget last September spooked the markets and sparked a huge economic fallout, pushing up government borrowing costs and putting certain pension funds on the brink of collapse.

One of the reasons for the markets' reaction was that Ms Truss and her chancellor, Kwasi Kwarteng, refused to publish the OBR's independent forecasts for the public finances alongside the plans.

The party said under its plans, ministers would be forced to open their books to the forecasters - though any government wanting to disregard them could seek to reverse the legislation.

It said families and businesses are "still paying the price" for her "crashing the economy" - with households coming off fixed rate mortgages paying an average of £220 more a month and inflation forecast to be the highest in the G7.

They have billed their proposal as a "fiscal lock" which would ensure fiscal stability by:

• Amending the legal framework governing the OBR to guarantee that where a fiscal event makes permanent tax and spending changes over a certain threshold, the fiscal watchdog can independently publish a forecast of the impact
• Setting out the threshold in a revised charter of budget responsibility, that would be voted on in parliament
• Ensuring that in the event of an emergency where changes must be introduced at speed and a forecast cannot be produced in time, the OBR would be allowed to set a date for when it can publish its forecast
• Setting out a fixed timetable for budgets that would say major fiscal decisions are announced by the end of November each year, allowing businesses and families four months to prepare for the new tax year and avoiding major changes to policy at the last minute
• Annual autumn budgets would be followed by a spring update in early March providing an updated forecast and minor policy changes

Speaking at the London Stock Exchange alongside Ms Reeves, Sir Keir said: "A year ago, huge damage was done to our economy and we're still paying the price. That can never be allowed to happen again."

The move would bring "stability for so many families that were affected by that disaster of a budget just a year ago," he added.

Labour has been seeking to pitch itself as fiscally prudent, prioritising stabilising the economy over big spending commitments in a move that has angered some unions and those on the left.

They have sought to weaponise the anniversary of the Truss mini-budget to hammer home their message of fiscal responsibility, while highlighting the government's record on the economy.

The plans received the backing of Tory former chancellor George Osborne, who urged Prime Minister Rishi Sunak to adopt Labour's proposal.

He said the Conservatives "created the OBR 13 years ago so chancellors couldn't any longer fiddle the numbers".

"A year ago we saw the fiasco when one tried to bypass it.

"These OBR reforms from [Rachel] Reeves are sensible, pragmatic improvements. If the Tories are smart they'll adopt them."

Ms Truss' £45bn package of unfunded tax cuts, which she admitted would primarily have benefited the wealthy, sent the pound tumbling, interest rates soaring and culminated with the Bank of England having to intervene to prevent pension markets from collapsing.

Although she rowed back on her measures and sacked her chancellor Mr Kwarteng, it was not enough to save her administration from collapsing and she resigned after just 49 days in the job - making her the shortest serving prime minister in British history.

She has remained unrepentant about the damage she caused, blaming "institutional bureaucracy" for her downfall.

Responding to Labour's plan she said it "beggars belief" they think "Britain's problems will be solved by bigger government and even more powers for quangos".

"Hard-working people and businesses - freed from overbearing regulation, tax, and debt - are going to get Britain growing again, not more bureaucrats in London," she claimed.

However, Labour hit back accusing her of having "no humility and no shame".

Darren Jones MP, Labour's Chief Secretary to the Treasury, said: "Weak Rishi Sunak needs to come clean with the public - does he agree with his ruinous predecessor or with Labour's plans to strengthen financial watchdogs?"