Labour has demanded Sajid Javid immediately publish economic forecasts prepared for the budget to ensure the government does not avoid public scrutiny before a potential election.

In a letter to the chancellor seen by the Guardian, John McDonnell called for the urgent release of forecasts compiled by the Office for Budget Responsibility (OBR), the independent Treasury watchdog.

He also demanded Javid set a new date for the budget, warning Britain’s standing in the world had been tarnished by the chancellor tearing up his plans for delivering tax and spending pledges on 6 November.

Q&A What is the Office for Budget Responsibility? Show Hide The Office for Budget Responsibility is the government’s independent forecaster, which gives its verdict on the outlook for growth and the public finances twice a year. The forecasts are published to coincide with the chancellor’s two big set pieces of the year – the autumn budget and the spring statement – and takes into account the impact of any tax and spending measures announced in those statements. The OBR also uses its public finances forecasts to judge the Treasury’s performance against the chancellor’s fiscal targets, stating whether or not it has a greater than 50% chance of hitting the targets under current policy. It was established in 2010 by the then chancellor George Osborne with the aim of improving the credibility of the government’s official forecasts for growth. The forecasts were previously produced by the Treasury itself and often criticised for being unrealistic. The OBR is led by three members of the budget responsibility committee, including chairman Robert Chote, a former director of the Institute for Fiscal Studies, with support from the OBR’s permanent staff of 27 civil servants.

“Inconsistency in decision-making in government over financial matters naturally adds to the current instability in the country’s affairs and its standing in the markets,” McDonnell wrote.

“It behoves the chancellor therefore to at least keep the public informed of the government’s intentions.”

Javid has come under mounting pressure to release the OBR health check since he confirmed his budget would be postponed. Economists warned voters would lack vital information to inform an election campaign.

James Smith, the research director of the Resolution Foundation thinktank, said: “The fact that the autumn budget has been scrapped is bad news for democratic debate in this country, as it means we are heading for the polls without up-to-date forecasts for the health of our economy and the public finances. This matters because the OBR’s forecasts provide crucial context for the promises that the parties will make during the election campaign.

“The hard work of producing these forecasts has already been done. The government should allow them to be published asap, irrespective of whether there’s an imminent budget or election.”

McDonnell said the OBR had probably already completed some of its forecasting work and shared the details with the Treasury, arguing in his letter to Javid that there was “no good reason why these should not now be made public”.

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The OBR last published an assessment of the economy and public finances in March. Since then, Boris Johnson has ramped up public spending while the economy has slumped close to the point of recession as Brexit uncertainty holds down growth.

The tax and spending watchdog must publish two forecasts in each financial year, under rules first introduced by George Osborne. They must be commissioned by the chancellor, although the OBR is understood to be considering what it would need to do to meet its requirements in the event the forecasts were not commissioned.

The Treasury is still understood to be planning to hold a budget and spring statement in the current financial year – key moments when the OBR would typically publish its forecasts – leaving Javid less than six months to comply.

A spokesperson for the Treasury declined to comment.