The reported security regime

Reports say Chancellor John Healey has brought defence habits into the Treasury, setting up what was described as "compartmentalisation" to keep financial secrets from escaping ahead of the budget. The comparisons with the armed forces began in mid-August, when the Telegraph reported Healey was "on a war footing" to stop information leaking. Other accounts added detail:

• The Financial Times reported "military-style protocols" were being deployed to protect budget information.
• The Spectator reported the use of "classified computer systems" for budget work.
• According to the i newspaper, officials' access was restricted so that each could reach only the section of the budget document on which they were working.
• The Observer reported Healey was "flabbergasted" by the lack of security around financial information when he became chancellor, comparing it unfavourably with the MoD.

Why secrecy was said to matter

Behind the lockdown, the report says, lay the chancellor's belief that market-sensitive leaks cost Britain billions in the run-up to the last government's budgets. He has also shut down speculation about possible tax rises, including higher capital gains tax on certain assets and lowering the mansion tax on properties worth more than £1.5m.

What leaked anyway

According to the report, the tightened security has not stopped the announcements: many budget measures have already emerged from a clear mixture of authorised and unauthorised sources. Among them:

• A higher tax on banks, described as a deeply market-sensitive policy, was disclosed in advance.
• A package of energy support for the most vulnerable came out before budget day.
• Billions of pounds in extra defence spending, directed towards the British Business Bank and National Wealth Fund, was pre-disclosed.
• A £1bn crackdown on online VAT sales will make big retailers such as Amazon, eBay and Temu responsible for collecting VAT due from smaller merchants selling on their platforms.
• Stories indicated the chancellor's fiscal headroom will be in the region of £15bn - known in the political trade as "pitch rolling".
• The Treasury and No 10 issued embargoed pre-budget announcements, including a new £1.5bn borrowing facility for local authorities and £1bn for social housing.

The case for and against a sealed budget

To former Treasury advisers, the secrecy partly deters civil servants and gossiping MPs before policies are ready.

But the same advisers caution that a budget sealed too tightly risks a backlash over unexpected measures - from markets, media, MPs and the public alike. The report points to past examples: George Osborne's pasty tax in 2012 was a less-trailed policy that went wrong, and Philip Hammond's surprise 2017 national insurance hike for the self-employed was abandoned within seven days after a furore among Conservative MPs over breaking a manifesto promise.

A former Tory strategist put the risk plainly: hoarding everything until the day leaves the chancellor with nothing but surprises.