The first major speech by the chancellor, Sajid Javid, has been mysteriously cancelled by the Treasury less than 24 hours before it was due to take place.

A Treasury spokesman said that the one-year spending review, called a spending round, which had been due to take place later this year, was now being fast-tracked to take place on 4 September – the date MPs return to parliament – adding fuel to speculation the government could be planning an early general election.

The speech, which was due to take place in Birmingham, was billed as Javid “outlining his vision for the UK economy”. In an email to attendees, the Treasury press office said the speech was being rescheduled but gave no other reasoning.

“The forthcoming Spending Round will instead be brought forward in early September and will cover the themes and priorities he was due to outline,” the email said.

It is understood the decision to cancel the speech was taken in Downing Street, rather than the Treasury. One source said it had been decided that Javid should make one speech on the government’s spending priorities once they had been agreed, not before, though that was denied by another source, who claimed the rescheduling was because the timing of the speech clashed with other prepared announcements.

Whitehall sources suggested there was considerable concern that MPs could trigger a vote of no confidence in the government and an early general election, which could lead to departments being left in the dark about spending plans, with budgets running out in 2020.

“We want people to be able to plan and there is a reason it is in early September because of the risks when MPs return to the house that week,” one source said.

Labour’s shadow chancellor, John McDonnell, said: “Sajid Javid is getting a record of announcing events and initiatives, and then within hours cancelling or reversing them. This doesn’t inspire confidence. Panic seems to be setting in inside government.”

The date of the spending round is expected to be announced shortly, most likely when MPs return to parliament next week. The 12-month review, instead of the usual three-year review, is intended as a short-term measure to give departments new budgets and also free up officials to focus on preparing for Brexit.

There is no legislation needed for the spending round, though there may be some supplementary votes on departmental spending.

In July, the Conservative MP Dominic Grieve, who opposes a no-deal Brexit, suggested an amendment in an estimates debate that would have effectively prevented the departments including education and work and pensions from accessing Treasury funds – effectively shutting down the government if the prime minister attempted no deal.

No 10 called that plan “grossly irresponsible” and the amendment was not selected by the Speaker of the House of Commons, John Bercow.