Boris Johnson has ordered an inquiry into the leak of his private text messages with businessman James Dyson.

The U-turn came less than 24 hours after Downing Street said no probe would be launched.

The prime minister’s official spokesperson said that the internal inquiry would be led by the Cabinet Office and is not intended for publication.

The national security adviser has not been asked to take part in the probe, and it is understood that neither the police nor security agencies have got involved.

The text messages, obtained by BBC political editor Laura Kuenssberg from an unknown source, showed Mr Johnson agreeing to try to “fix” tax problems experienced by Dyson staff working on the development of ventilators in the early stages of the Covid-19 pandemic last spring.

Downing Street said that the inquiry will not consider a separate leak of text messages from Saudi Crown Prince Mohammed bin Salman asking Mr Johnson to intervene in the proposed takeover of Newcastle United FC.

Mr Johnson’s spokesperson confirmed that the prime minister remains committed to his promise to MPs on Wednesday to release details of his contacts with Mr Dyson.

But he was unable to name a date for the release, saying only that it would happen “shortly”.

Soon after the leak on Wednesday, the spokesperson told a Westminster media briefing that there was no plan for a leak inquiry.

The failure to order an immediate probe prompted speculation in Westminster that the PM may believe he already knew who was behind the security breach but prefer not to risk further publicity by mounting an inquiry.

His spokesperson said today: “As usual, we keep these things under review and we have decided to undertake this internal inquiry.

“As you would expect, we continually look at these things and the position we decided today is that we want to make sure we have this internal inquiry.”

The spokesperson declined to explain why the Crown Prince’s texts were not also included in the probe, telling reporters only that “we are looking into this specific incident”.

He refused to comment on reports that Mr Johnson had been advised to change his mobile phone number because he was being contacted so regularly on it by business figures and other people outside government.