"As David Davis boards the plane to negotiate Brexit on behalf of the Government, it is unclear what the Government's position actually is". If she waters down her exit strategy - as her predecessor, David Cameron, has urged her to consider - that could set off a rebellion from hard-line "leave" supporters, including David Davis, the Cabinet minister responsible for negotiating Britain's withdrawal, and the foreign secretary, Boris Johnson.
He said: 'You can only be a full member of the single market if you are an European Union member and therefore it is obvious that we are looking for something else. But the turmoil of the euro zone crisis, fears in Britain about immigration and a series of miscalculations by former Prime Minister David Cameron prompted Britain to vote by 52 to 48 percent for Brexit in a June 23 referendum past year.
There is lots of talk about what Philip Hammond wants, and how he might seek to "soften" Brexit.
Three days after the talks begin, May is due to travel to Brussels for an European Union summit - a chance for the other 27 leaders to take stock of their negotiating partner in the sharply altered climate brought about by the dramas of the past two weeks.
"We have come together to urge the government to put the economy first as it prepares to start formal negotiations on the UK's departure from the European Union", says the statement from the BCC, CBI, manufacturers' group EEF, the Federation of Small Businesses and the Institute of Directors.
During an interview on the Andrew Marr Show, Sir Keir said Britain could not stay in the single market in "an unreformed, unchanged way" - but sidestepped questions on the details, saying it is more important to focus on the outcome.
Britain's Brexit ministry said the team travelling to Brussels was confident it could achieve a "bold and ambitious deal" and forge a new, close arrangement with the bloc.
"We will build the broadest possible consensus for our Brexit plans and that means giving parliament the maximum amount of time to scrutinise these bills by holding a two-year session of parliament", the government said in a statement.
USA environment chief leaves G-7 climate talks early
Trump said earlier this month he intends to withdraw the US from the agreement unless it can be renegotiated. Pruitt left early to attend Trump's first full Cabinet meeting on Monday.
European Union officials see the start of Brexit talks on Monday as a sign Theresa May is accepting their format for negotiations but they expect no quick deals and are wary the prime minister may try to break with Brussels protocol.
Mr Hammond also warned about failing to get a Brexit deal.
With Scotland poised to trigger a second referendum, and the threat of renewed hostilities in Ireland at the prospect of a hard border between Northern and southern Ireland - could Brexit spell the end of the United Kingdom?
The fact that May has to rely on the Democratic Unionist Party in order to govern - when the British government has to play the role of the honest broker in Northern Ireland - might also cause problems. Divorce talks are set to begin next week as the anniversary of the Brexit vote nears.
Thus whether Brexit can be halted or not depends primarily on the UK's government and people.
The point is she is not a unifying figure any more.
Mr Davis's agreement to Monday's agenda led some European Union officials to believe that Mrs May's government may at last coming around to Brussels' view of how negotiations should be run.
"We should be protecting jobs, protecting economic growth and protecting prosperity", he said in Luxembourg last week.