With one year to go until Brexit, Theresa May is mounting a whirlwind tour of the UK and Northern Ireland with a promise to keep the country "strong and united".
Speaking to voters in England, Scotland, Northern Ireland and Wales, Mrs May will say that, whether they voted Leave or Remain, what is important now is making Brexit "a success for everyone".
Mrs May is set to have lunch with farmers near Belfast later today.
Sinn Féin has criticised today's visit.
The party is highlighting the fact Mrs May will not be meeting with any of the northern parties.
The British PM's bid to heal divisions caused by the 2016 EU referendum comes as polls suggest voters are still split down the middle over whether or not the UK should leave.
As the final year countdown began, she was buoyed by the EU's approval for a 21-month transition period after the official date of Brexit on March 29 2019 to allow the UK to prepare for its new relationship with Europe.
But tough negotiations on the nature of the future relationship lie ahead over the months before a planned agreement in the autumn.
And the UK Government is facing stiff resistance from Edinburgh and Cardiff to plans to repatriate some powers from Brussels to London, rather than the devolved administrations.
Speaking ahead of her trip, Mrs May said: "I am determined that our future will be a bright one. It's a future in which we trade freely with friends and partners across Europe and beyond.
Mrs May insisted that each of the devolved administrations will see "an increase in their decision-making powers" as a result of the return of responsibilities currently exercised by the EU.
Her Government remains "absolutely committed" to the devolution settlements, she said.
And she restated her rejection of EU proposals which would effectively create an administrative border down the Irish Sea by keeping Northern Ireland in the Customs Union.
"As the Prime Minister of the United Kingdom, I have an absolute responsibility to protect the integrity of the United Kingdom as a whole," she said.
"No Prime Minister could leave these things to chance, because they are absolutely crucial to our success as a country in the future."
Mrs May said the Union delivered "enormous benefits" to all four nations of the UK.
And she declared: "I am determined that as we leave the EU, and in the years ahead, we will strengthen the bonds that unite us, because ours is the world's most successful union.
The British PM will start the day by visiting textile workers at a factory in Ayrshire, before travelling to Newcastle to meet with a local parent and toddler group.
She will have lunch with farmers near Belfast before travelling to Barry in south Wales for a round-table discussion with businesses, and will later have tea in west London with a group of Polish citizens who have made the UK their home.
But the news has not been universally welcomed.
Michael Russell, Scottish Minister for UK Negotiations on Scotland's Place in Europe, said: "By pursuing a disastrous hard Brexit, regardless of the cost to jobs and living standards, Theresa May and the Tories have shown they think they can now do anything to Scotland and get away with it.
"Instead of treating Scotland as an equal partner, the UK Government wants to conduct a power grab on the Scottish Parliament, which is being strongly resisted by every party apart from the Tories."