Energy Secretary Grant Shapps appointed defence secretary, replacing Ben Wallace who had previously said he would quit
Shapps pledges to continue supporting Ukraine following Russia's "barbaric invasion"
Education minister Claire Coutinho is promoted to cabinet as energy and net zero secretary, replacing Shapps
Ukrainian defence minister Oleksii Reznikov paid tribute to Wallace, saying he "led by example"
The former defence secretary, who was in the job for four years, played a key role in the UK's response to the war in Ukraine
Back in February, Defence Secretary Ben Wallace told the BBC the UK needed to start "investing in defence properly".
He said the army had been "hollowed out" over a period of 30 years and the Ukraine war had "exposed our vulnerabilities".
UK and European officials have raised concerns over the state of the British armed forces.
Chris Mason
Political editor
Image source, PA MediaEnergy Secretary Grant Shapps is expected to be named by Prime Minister Rishi Sunak as his new defence secretary shortly.
The Labour Party says outgoing Defence Secretary Ben Wallace has shown "important leadership in supporting Ukraine from the start" following his resignation in the last hour.
In a statement, a party source said: "Labour will continue to stand shoulder to shoulder with the government in support of the people of Ukraine until the war against Russia is won.
"We have to stay the course and see this through."
But there was also criticism from the opposition, saying his record on the British armed forces "has been poor".
Quote MessageThe new defence secretary needs to get a grip, boost British forces and give them the resources, kit and accommodation they deserve."
Labour Party source
Energy Secretary Grant Shapps, who has not been one of the names mentioned as a possible replacement for Ben Wallace, has arrived at No 10 Downing Street.
Could he be Rishi Sunak's pick for the boss of the MoD? Stay with us as we find out together.
Ben Wallace said last monthhe would quit his post at the next reshuffle of government ministers, and leave Parliament at the next general election.
Wallace has served continuously as a minister under five prime ministers, having originally been appointed by David Cameron as a government whip in 2014.
He went on to be a Northern Ireland minister, security minister and has been defence secretary since July 2019.
Earlier this year he was tipped to be the new Nato secretary general, but, in June, he told the Economist, external: "It's not going to happen."
Despite his obvious enthusiasm to succeed current Nato chief Jens Stoltenberg as the next head of Nato, Wallace appears to have failed to get the backing of key allies to secure the top job.
In July. Stoltenberg’s mandate was extended until 1 October 2024.
James Heappey and Liam Fox are two of the well-known names in the frame for the post of Defence Secretary.
Heappey, the current Armed Forces Minister, is a former soldier who served in Afghanistan. He has been an MP since 2015. Heappey endorsed former PM Boris Johnson during the 2019 leadership election, and went on to serve as his parliamentary private secretary.
The Daily Telegraph claims, external Liam Fox - who was defence secretary in 2010 under Prime Minister David Cameron - is also a "leading candidate" for the job.
Fox was an ardent supporter of Prime Minister Rishi Sunak during his campaign for the Conservative leadership in 2022.
He stepped down from the role of defence secretary 12 years ago, after it emerged the best man at his wedding, Adam Werritty, joined him on 18 foreign trips and handed out business cards suggesting he was his adviser - despite having no official role.
Chief Secretary to the Treasury John Glen is another name touted as a possible successor to Wallace.
The former management consultant has held a number of government roles including parliamentary under-secretary for arts, heritage and tourism (2017-18) and city minister (2018-22).
Downing Street has refused to comment on who might replace Wallace.
Image source, ReutersBen Wallace formally submitted his resignation to the prime minister this morning.
Let's have a closer look at the letters which were exchanged between the prime minister and Ben Wallace back in July.
In his letter to Rishi Sunak, Wallace wrote: "The Ministry of Defence is back on the path to being once again world class with world class people.
"The United Kingdom is respected around the world for our armed forces and that respect has only grown more since the war in Ukraine.
"I know you agree with me that we must not return to the days where defence was viewed as a discretionary spend by government and savings were achieved by hollowing out."
The PM praised Mr Wallace in his response telling him the defence secretary leaves the office with his "thanks and respect".
Thomas Mackintosh
Live reporter
Good morning and welcome along to our political coverage this morning as Rishi Sunak looks poised to appoint a new defence secretary.
Last month Ben Wallace announced he wanted to leave the post, bringing an end to his four years in the job. This morning he formally quit the job - meaning the PM will announce his successor shortly.
A number of Conservative MPs are rumoured to be in the running to head up the Ministry of Defence.
We'll have our team bringing you the latest updates, analysis and reaction - so do stay with us.