Foreign Secretary Liz Truss has launched a bid to succeed Boris Johnson as party leader and prime minister.
Announcing her plan to run in the Daily Telegraph, Truss told the paper she would cut taxes from "day one", should she become prime minister.
The race widened significantly over the weekend, with many leadership hopefuls setting out competing tax plans as a core element of their pitches.
But there are divisions over the timing and scale of the proposed reductions.
She also indicated she would join her rivals in planning to slash corporation tax, reverse the National Insurance hike and reform business rates.
Truss told the paper she would "fight the election as a Conservative and govern as a Conservative", adding she would also take "immediate action to help people deal with the cost of living".
The 1922 Committee of backbench Tory MPs will set out later today the timetable for the leadership election.
A flurry of weekend announcements has seen most - but not all - candidates promise lower rates for individuals, businesses, or both, as tax emerges as a key battleground.
So far the list of contenders for the leadership includes:
- former equalities minister Kemi Badenoch
- Attorney General Suella Braverman
- newly appointed Foreign Office Minister Rehman Chishti
- former health secretary Jeremy Hunt
- former health secretary Sajid Javid
- Trade Minister Penny Mordaunt
- Transport Secretary Grant Shapps
- former chancellor Rishi Sunak
- backbencher Tom Tugendhat
- Chancellor Nadhim Zahawi
The slew of tax-cutting plans to have been announced so far mark a contrast with Sunak, who has played down the prospect of tax cuts before public finances improve.
The former chancellor has not yet set out his economic pitch for the leadership, promising more details in the coming days and weeks.
But in a video launching his campaign, he warned against "comforting fairy tales" that would "leave our children worse off tomorrow".
Truss cut short a trip to the G20 summit of wealthy nations being held in Bali, Indonesia, last week to fly back to the UK following Johnson's resignation as Tory leader.
She has served under three Conservative prime ministers since being elected in 2010.
Truss was environment secretary in David Cameron's government from July 2014 to June 2016 and justice secretary under Theresa May from July 2016 to June 2017.
Tax has emerged as the key pledges for many of the candidates, but questions have been raised about how they will be paid for.
Zahawi, who became chancellor last week, joined the chorus of leadership hopefuls in calling for lower taxes in an fresh interview with the Telegraph, telling the paper "nothing is off the table".
A spokesman also promised that Zahawi - who has faced claims that his tax affairs have been investigated - would publish his tax returns should he become one of the final two candidates in the race.
Experts have raised questions about the ability of a new prime minister to slash taxes without affecting public spending.
Paul Johnson, director of the Institute for Fiscal Studies think tank, said predictions of a budget surplus of about £30 billion ($NZ58b) by 2024 were calculated at a time when inflation predictions were lower.
Writing on Twitter, he added that using the headroom to fund tax cuts would "almost certainly" require public sector pay cuts or more borrowing.
"Everyone would like lower taxes. But [we] need to be clear about consequences," he added.
Meanwhile, Labour leader Sir Keir Starmer is set to take aim at the leadership hopefuls for signing up to "unfunded spending commitments", describing them as taking part in an "arms race of fantasy economics".
In a speech set to be delivered in a few hours, Sir Keir is also expected to criticise them for now opposing tax rises introduced by Johnson and Sunak, after voting for them previously.
-BBC