Cabinet Office minister and deputy chief whip resign from government

Chloe Smith and John Randall have both resigned from the government. Photograph: Composite

David Cameron's long-serving deputy whip, John Randall, and his youngest minister, Chloe Smith, have resigned ahead of a reshuffle in which the prime minister is expected to promote a number of women.

Downing Street's surprise announcements sparked speculation that Cameron will shake up junior roles within his team as early as Monday. They follow the resignation of transport minister Simon Burns, who wants to stand as deputy Commons speaker, with rising stars such as Sajid Javid, Esther McVey and Nicky Morgan tipped for bigger jobs.

Randall, who has served in the Tory whips' office for 13 years, said he informed the prime minister last year that he wanted to return to the backbenches. He is best known for his role in the resignation of his boss, Andrew Mitchell, the former chief whip, over the "plebgate" scandal just over a year ago.

Randall passed on information about Mitchell's alleged behaviour after one of his constituents claimed to have witnessed the former minister swearing at police officers and calling them "plebs". Mitchell always strongly denied the accusations and the constituent turned out to be a serving officer, who was later arrested as part of a wider investigation into an alleged conspiracy.

In his resignation letter, Randall assured the prime minister that he would continue to do "whatever I can for you personally as well as for the party, the government and of course the country".

"I know that it is customary to write at these times that it has been a great privilege and honour to serve as a member of the government, but it really has been that and a lot more," he wrote. "I have served 13 years in the whips' office both in opposition and more recently in government and I have served under and with some fantastic colleagues, notably Patrick [McLoughlin] and Sir George [Young], who have made the job extremely worthwhile and even fun."

Cameron's reply to Randall was glowing, describing him as a "rock" for the whips' office and the parliamentary party. "It sounds dramatic, but I had rather hoped this day would never come," Cameron wrote. "I could not have wished for a more loyal, discreet, patient, trustworthy and committed colleague over the last eight years since I became leader of the party, but you have been all these and much more."

Smith, a Cabinet Office minister, is stepping down to concentrate on her constituency work and engaging young people in politics. The 31-year-old MP, who has previously served as a whip and a Treasury minister, has recently been overseeing the controversial lobbying bill, which has been criticised by charities and campaign groups as posing a potential threat to freedom of speech. She was moved from the Treasury in the last reshuffle shortly after a difficult interview on BBC Newsnight about the chancellor's deferral of fuel duty.

Smith, the MP for Norwich North, told the Guardian that her choice to step down was "to do with priorities and what's most important".

"Essentially, it's entirely my own decision and something I see as very positive," she said. "Anyone who has known me and my work has known that my constituency comes first. It's the case that I've spent three of my four years in parliament serving as a minister. I'm very proud of that and achieving various things, like helping to save £10bn pounds of Whitehall waste. But for now I want to focus on the things that really matter to me."

In her resignation letter to Cameron, she said: "As you know, I was only 27 when I was lucky enough to be elected as an MP, and of my four years in parliament so far, I have spent three as a minister. I would welcome the opportunity to develop other ways of giving public service, both inside and outside parliament, while continuing to work hard for my constituents."

The prime minister's reply said Smith has served "ably" and made a "positive impact". "I know this will not have been an easy decision for you to make, and one you will have given a huge amount of thought to," he said.

"After serving the government so ably for over three years, you will certainly be missed, but I completely understand and respect your decision."

The Tory reshuffle could happen at the same time as Ed Miliband shakes up the Labour frontbench. He is thought to be considering moving the shadow health secretary, Andy Burnham, and the shadow work and pensions secretary, Liam Byrne, with shadow Treasury minister Rachel Reeves tipped for promotion.