During the Battle for Number 10 debate, Mrs May praised being called a “bloody difficult woman” by Kenneth Clarke last year.
The Prime Minister said that Mr Clarke had use the term because "he saw me as somebody who stood by what I thought was right and was willing to fight for what I believe is the right thing to do".
She added: "That's what drives me. Doing what is the right thing by the country. Sometimes you have to be difficult in order to do that.
Theresa May renewed her vowed to be a difficult woman for British interests
Theresa May was quizzed by Jeremy Paxman about the 'bloody difficult woman' mantra
"But if I look at what is coming ahead for this country, we stand at a very important moment in our history.
"We have the opportunity now to really change this country for the better for the future."
The Prime Minister promised she would use the mantra when dealing with domestic issues like the ageing population, divisions within society, changing technology and economic growth.
Theresa May's political career in pictures Tue, April 18, 2017
Prime Minister Theresa May has promised to 'build a greater Britain'
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Saudi Arabia's King Salman bin Abdulaziz al-Saud (R) meeting with British Prime Minister Theresa May in the capital Riyadh, Saudi Arabia, 05 April 2017. May is visiting Saudi Arabia as part of her Middle East trip to boost diplomatic ties in the region
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What I'll be doing is being a difficult woman and ensuring we're negotiating hard
Mrs May said: ”We need to have a Government that is open about these things and is willing to find ways of addressing them.
"If in order to address them and do the right thing by the country, it takes being a difficult woman, then that's exactly what I will be."
She added: "Some of them will involve difficult choices, but I think it's right if I'm saying to people I want a mandate to be Prime Minister and have the Government of this country, that we are open with people and say there will be hard choices."
Mrs May said she was prepared to make difficult choices Theresa May awkwardly eating chips could be 2017's 'bacon sandwich' Tue, May 2, 2017
Theresa May suffered what has been suggested to be her “bacon sandwich” moment after pausing for a quick snack while on the campaign trail
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Britain's Prime Minister Theresa May eats chips as she meets with residents in Mevagissey, south-west England, on May 2, 2017, during a campaign visit ahead of the forthcoming elections
Mrs May also renewed her pledge to be “bloody difficult woman” in Brexit negotiations and vowed to walkaway if the Brussels bloc offered the Britain a bad deal.
She said: "It isn't a question of what it's worth paying to get out, it's a question of what is going to be the right deal for us to leave the European Union, which will stop us from paying huge sums of money into the EU every single year, which will enable us to have control of our money, of our borders and our laws."
When asked whether she was prepared to walk away without a Brexit deal, Mrs May replied: "I think you have to. In negotiations you have to recognise that you're not in there to get a deal at any price.
"We're in there to get the best deal for the United Kingdom, and actually I'm optimistic about that because I think in the European Union they want to continue their relationship with us as well."
She added: "What I'll be doing is being a difficult woman and ensuring we're negotiating hard."