Mr Shapps, who has held five ministerial jobs in the past year.  His appointment was not widely expected but he is seen as safe pair of hands and an effective communicator.

Sunak ally Claire Coutinho replaces him as energy secretary. It is a major promotion for Ms Coutinho, who has only been an MP since 2019 and, at 38, will be the youngest minister to sit around the cabinet table.

She is seen by colleagues as bright and competent – but she faces a tough task in holding the differing wings of her party together over the government’s commitment to net zero.

Labour’s shadow climate change secretary Ed Miliband said her appointment “speaks volumes about the failures of Tory policy that we are now onto the sixth secretary of state since 2019”.

“Reshuffling of the deckchairs will not deliver the proper energy policy Britain needs,” he added.

Some Tory MPs had expected Mr Sunak to carry out a more wide-ranging reshuffle, ahead of next month’s Conservative Party conference and the King’s Speech, setting out the government’s priorities.

But the prime minister, who had to replace Ben Wallace after he announced he was standing down as defence secretary, has opted to play it safe for now.

Some expect a wider reshuffle before the next general election, although some Tories fear the PM may run out of time.

In his first statement as defence secretary, Mr Shapps said was “honoured” to take on the role and pledged to “continue to UK’s support for Ukraine”.

Mr Shapps paid tribute to the “enormous contribution Mr Wallace has made to UK defence and global security over the last four years”.

“I am looking forward to working with the brave men and women of our Armed Forces who defend our nation’s security,” he added.

Mr Shapps has held seven cabinet roles since 2012.  Last October, he spent six days as home secretary during the final chaotic week of Liz Truss’ premiership, following the resignation of Suella Braverman from that role.

He was then appointed business secretary by Mr Sunak, when he became prime minister after Ms Truss.

Mr Shapps’ longest stint in government has been as transport secretary where he negotiated repeated bailouts for Transport for London during the Covid-19 pandemic.

Since Russia’s invasion of Ukraine, Mr Shapps has taken a visible role in the UK’s support of the country.  He took part in the Homes for Ukraine scheme, hosting a family of refugees at his Hertfordshire home.

Mr Shapps visited Ukraine last week, in his previous role as energy secretary, to highlight the UK government’s role in guaranteeing a supply of enriched uranium to the country’s nuclear power plants.

Mr Shapps lack of experience in foreign affairs, defence and security has concerned some Conservative MPs and army figures.  One anonymous minister said Mr Sunak had gone for “media over capabilities. The ‘minister for the Today Programme’ is the minister for defence,” they added.

Former head of the British army Lord Dannatt said: “The big question is whether Grant Shapps is going to be a political appointee to support the prime minister in cabinet or is he going to understand the needs of defence.

“He will have to work really hard to understand his portfolio at a Whitehall level and how the armed forces work.”

Labour’s shadow defence secretary John Healey congratulated Mr Shapps on his appointment.  He said he would work with his opposite number “to keep our country safe” – but added that “after 13 years of Tory defence failures, a change at the top will not change this record”.

Liberal Democrat defence spokesperson Richard Foord said Mr Sunak had appointed a “yes man”, who will be in charge of “slashing troop numbers by 10,000”.

“They have taken the armed forces for granted for too long, and we are all left less safe as a result,” Mr Foord said.

David Johnston, a Tory backbenches, takes over Ms Coutinho’s role as children’s minister at the Department for Education.

Mr Wallace, who served as defence secretary for four years under three prime ministers, said he was stepping down “to invest in the parts of life that I have neglected, and to explore new opportunities”.

In his resignation letter, Mr Wallace said his military and political careers has come at “a personal toll to me and my family”.

Mr Wallace leaves parliament as one of the longest serving ministers in government.

As defence secretary he oversaw the evacuation of personnel from Afghanistan. He became a high-profile and ardent supporter of Ukraine after Russia launched its full-scale invasion in February 2022, cajoling other nations to respond to President Zelensky’s call for weapons to repel the Russian threat.

He also called for an increase in forces funding claiming the British army had been “hollowed out” over 30 years.

Ukrainian Defence Minister Oleksii Reznikov said Mr Wallace “led by example” whose work “inspired other countries to join in assisting Ukraine”.

In a statement Mr Reznikov said he wants to thank his “friend and colleague” for “everything he has done for Ukraine while in his position”.