Boris Johnson has seized control of the Treasury as part of a plan to create a single base of power

The prime minister has asserted his power as the first lord of the Treasury in a bold coup aimed at restructuring the heart of government

To what end has Boris Johnson so brutally asserted his authority over the Treasury? The most likely explanation is that he felt Sajid Javid was too cautious about the government’s plans for big projects and high spending on public services.

It seems the prime minister deliberately forced Javid out by making the impossible demand that he sack all his special advisers. But that demand was part of a plan to integrate the Treasury and No 10 as a single centre of power devoted to delivering Johnson’s programme.

Whether or not Johnson intended Javid to resign, it seems the prime minister has got rid of one of the weakest chancellors in modern times in order to install one he regards as more reliable. Rishi Sunak was chosen by Johnson to represent him in the TV debates during the election: his performance was smooth and forgettable, but, as we now see, a triumphant success.

This could have two contradictory consequences. One is that it makes 10 Downing Street more powerful than it has ever been, in the eternal balance of power between prime minister and chancellor. If Johnson wants to change the rules on rates of return on investment for big transport schemes, for example, he will be able to do so.

But the other consequence is that it makes Rishi Sunak, the new chancellor, potentially powerful in the future, because he will be part of a combined centre of government charged with delivering for its voters. If it starts to succeed, Sunak’s status will be enhanced; he will become unsackable; and may be talked about more and more as a possible successor to Johnson himself.

British history suggests that the tension between prime minister and chancellor can never be abolished. David Cameron and George Osborne came closest to doing so, but they had the counterweight of the Lib Dems in coalition – when that was lifted in the 2015 election, everything started to go wrong.

Johnson will not succeed in permanently asserting his authority as first lord of the Treasury over such a powerful department. William Gladstone might have done it in the 19th century, but in the 21st a prime minister will always want to spend money and the Treasury as an institution is bound to resist, on behalf of taxpayers.

For the moment, though, Johnson has the power. He wants to deliver dramatic improvements in public services, especially in those midlands, northern and Welsh constituencies that voted for him for the first time.

Dominic Cummings, his chief adviser – another big beneficiary of today’s reshuffle – has long talked of restructuring the institutions of government to focus on project management. What we didn’t think he meant was reordering the structure of the heart of government: No 10, the cabinet office (which acts as a kind of prime minister’s department) and the Treasury.

Tony Blair tried to create a powerful, delivery focused centre at the heart of government, that would have strengthened his power as prime minister, but he came up against the immovable object of Gordon Brown – and in the end Blair never thought it was in his interest to force his chancellor out.

Johnson starts from a very different position, but I suspect he will find the Treasury will reassert its power eventually, because it controls the money.