Theresa May is expected to name a 'Minister for a No Deal Brexit' as a reshuffle of her cabinet began with confusion.
In what appeared to be the first change to be announced, a tweet posted by the Conservative Party revealed that Transport Secretary Chris Grayling had been made chairman of the Conservative Party, replacing Sir Patrick McLoughlin.
However, it was deleted within seconds, with the Immigration Minister Brandon Lewis later confirmed as taking on the important internal role. James Cleverly has been named as Mr Lewis’ deputy, with MPs from the 2015 and 2017 intakes also appointed to help rejuvenate the Conservative Party’s grassroots operation.
Meanwhile, the Northern Ireland Secretary James Brokenshire has resigned on health grounds.
It was reported that one of the junior ministers in the Department for Exiting the EU could be given responsibility for getting the UK ready in case talks in Brussels fail to reach a deal, and could attend cabinet alongside Brexit Secretary David Davis.
Reports suggest that around half a dozen of her senior ministers could be axed or moved, with Number 10 sources indicating the more junior ministerial appointments would continue into a second day on Tuesday.
The most senior members of the Government - Chancellor Philip Hammond, Foreign Secretary Boris Johnson, Home Secretary Amber Rudd and Mr Davis - will all remain in their present posts.
However Education Secretary Justine Greening, Business Secretary Greg Clark and the Leader of the Commons Andrea Leadsom are all reported to be vulnerable as Mrs May seeks to assert her authority.
Sir Patrick was widely tipped to pay the price for the party's failure at last year's snap general election when the Tories saw their Commons majority wiped out.
The Justice Secretary David Lidington has been named Minister for the Cabinet Office, and will replace Damian Green as the government’s lead minister in Brexit talks with devolved administrations.
However, while Downing Street said Mr Lidington would stand in for the Prime Minister at PMQs, he has not been given the formal title of First Secretary of State, a role which effectively gave Mr Green the role of deputy Prime Minister.
Mr Green was forced to resign last month after admitting he lied over allegations pornographic material was found on his Commons computer during a police raid in 2008.
It is thought that Mrs May will take the opportunity to bring forward some more junior ministers, with Justice Minister Dominic Raab among those tipped for promotion.
The Prime Minister is also believed to want more women and MPs from ethnic minorities in her team with Suella Fernandes, the leader of the backbench Eurosceptics, Seema Kennedy and Rishi Sunak among those who could enter the Government for the first time.
Overall the reshuffle will be more extensive than that carried out by Mrs May following her humiliation in last year's general election when she felt able to make only limited changes to the Cabinet.
Speaking at the weekend, Mrs May insisted she still wanted to lead her party into the next election due to take place in 2022, declaring: "I'm not a quitter. I'm in this for the long term."
But pressed on whether she would still be there the next time the country goes to the polls, she appeared to acknowledge that the decision may not be entirely down to her, saying: "Obviously I serve as long as people want me to serve."
A source close to Mr Brokenshire said he had decided to stand down because he was facing major surgery within the next couple of weeks. The Old Bexley and Sidcup MP is a close ally of Mrs May, having served under her for five years at the Home Office, and he was not among ministers who were predicted to go in the Prime Minister's first major reshuffle since she took office.
Explaining his decision, a source close to Mr Brokenshire said: "He has a small lesion on his right lung and is getting major surgery in the next couple of weeks."