"But we will still be neighbours, we still be part of the European family of nations, and we will continue to champion the same beliefs - standing for freedom, democracy and the rule of law, underpinned by a rules-based global order", she will say.
Asked who spoke for the Labour Party on Brexit, Mr Watson told Radio 4's Today programme: "Well, very thankfully, for me personally, it's Keir Starmer, the shadow Brexit secretary, and I thought he did a brilliant speech yesterday, I thought the conference united around him".
He repeated Labour's argument that if parliament rejects May's Chequers deal, named after the prime minister's country residence where she hashed out a plan with her ministers, the party would press for a general election.
She said of the EU: "If they have concerns they need to detail those concerns, and if they have counter-proposals let's hear the counter-proposals and then we can discuss those and take them forward".
And David Mallon, a delegate from the North East, was embraced by party leader Jeremy Corbyn after opposing a second referendum and describing the European Union as a "capitalists' club".
Sir Keir released an analysis of the Brexit blueprint agreed by the Cabinet at Mrs May's country residence, which he said showed it failed to pass Labour's six tests.
May promised last week that even if Brexit negotiations with the EU break down, the rights of Europeans now living in Britain "will be protected". An EU summit next month is seen as a make-or-break moment for a Brexit deal.
The U.S. Federal Reserve is expected to raise interest rates for the third time this year later on Wednesday, and investors will be looking for clues as to whether the central bank will ramp up the pace of policy tightening following signs of an acceleration in U.S. economic growth.
Labour party leader Jeremy Corbyn has long opposed the idea of a new Brexit referendum, saying the party must respect voters' decision to leave.
Stressing that Labour's priority in any Brexit deal was to protect jobs, manufacturing industry, living standards and workplace and environmental protections, Mr Corbyn denied that his stance was letting down Labour supporters who backed Leave.
Even if May is able to secure a deal on Brexit with Brussels, it is far from certain she will be able to get the terms approved by parliament. It just feels like it's just that one more step and we're there.
Starmer has said a referendum to reverse Brexit must be an "option", but Corbyn's position is less clear.