Chancellor George Osborne will move to try to calm market turmoil triggered by the pro-Brexit vote as Boris Johnson broke cover in a bid to start healing Tory wounds ripped open by the bitter referendum battle.
Mr Osborne will speak ahead of the start of financial trading on Monday, and outline how the Government will "protect the national interest" after its humiliating defeat in the landmark nationwide poll.
"The Chancellor will make a statement ?to provide reassurance about financial and economic stability in light of the referendum result and the actions that he and the rest of the Government will be taking to protect the national interest over the coming period," a Treasury spokesman said.
The move follows unprecedented simultaneous upheaval in both major political parties with outgoing premier David Cameron's resignation plunging the Tories into a battle of succession, as Labour leader Jeremy Corbyn faces down a mass shadow cabinet walk-out aimed at toppling him.
Still holding back from formally announcing his bid for the Tory crown, frontrunner for Number 10, Mr Johnson used his Daily Telegraph column to concede Leave only managed a "narrow majority" and must now reach out to ease the fears of the 16 million people who voted Remain.
Amid clamour for the Leave campaign's leaders to set out what happens next, Mr Johnson claimed Britain will be able to introduce a points-based immigration system while maintaining "access" to the European single market.
"The only change - and it will not come in any great rush - is that the UK will extricate itself from the EU's extraordinary and opaque system of legislation: the vast and growing corpus of law enacted by a European Court of Justice from which there can be no appeal. This will bring not threats, but golden opportunities for this country - to pass laws and set taxes according to the needs of the UK," he wrote.
Mr Osborne is desperate to head off a repeat of the run on the pound and global stock market plunge which was provoked by the unexpected pro-Brexit vote.
The Chancellor is also under pressure to set out a timeline for opening negotiations with the EU on the terms of Britain's "divorce" from the EU.
Mr Cameron has insisted his successor should be the one to invoke article 50 of the Lisbon Treaty which sets in train formal withdrawal procedures after he leaves Downing Street in October.
But EU leaders are becoming increasing impatient with this proposed delay as they insist the UK has opted to quit and needs to be out of the bloc as soon as possible.
Pro-Brexit leaders had hoped to hold informal talks with the EU before triggering the strict two-year timetable for exit set out in the isbon Treaty, but Brussels is hostile to the idea.
Mr Osborne will also need to clarify whether he will try to bring in the so-called "punishment Budget" comprising of £30 billion worth of tax rises and spending cuts that he insisted during the referendum campaign would be necessary in the event of the UK voting for Brexit.
Mr Corbyn and pro-Brexit Tory MPs made it clear that they would not vote for such a financial package if Mr Osborne tried to get it through the Commons.