Theresa May will pledge to form a more "united" Britain as the Brexit process begins.
The Prime Minister is to make a keynote speech at the Conservative Spring Forum in Cardiff, where she is due to speak more about her plans for Brexit.
Mrs May is expected to say: "The coming negotiations with the EU will be vital for everyone in the United Kingdom.
"We are four nations, but at heart we're one people.
"I will always ensure the voices of England, Scotland, Wales and Northern Ireland are represented as we negotiate to leave the European Union.
"I will always fight to strengthen and sustain this precious union."
This speech comes at the end of a difficult week for the Prime Minister and the Conservative Party.
Earlier in the week her Chancellor, Phillip Hammond, conducted an embarrassing u-turn over his planned national insurance hike and on Thursday, the party was hit with a £70,000 fine for failing to properly declare election expenses.
The speech also comes just a day after Mrs. May angered Nicola Sturgeon and the Scottish National Party for saying "now is not the time" for a second Scottish independence referendum, ahead of the exit negotiations with the EU.