The 35-year-old aims to reach out to the 13.6 million people who voted to leave the European Union, but who did not feel able to support UKIP at last year’s General Election.
He said: “These people voted for Brexit in a democratic election and our Government must be held to account, to ensure that ‘no’ really does mean ‘no’ and that Brexit really does mean Brexit.
“It is increasingly clear, following Andrea Leadsom’s abandoning the race to become Prime Minister, that the establishment is organising itself for ‘business as usual’. Worryingly, under the new Prime Minister Theresa May, negotiations for the UK’s withdrawal from the EU will be in hands of those who do not actually want us to leave.
“The Labour Party is of course in complete disarray, so quite frankly Ukip represents the only alternative to the establishment and will be the only unifying force for Brexit.
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“Since June 23, the entire DNA of UKIP has changed. We are no longer a party of protest, but a party of the future. There are many challenges that lie ahead, but first we must hold the government’s feet to the fire to enact the will of the 17.4 million people who voted for Brexit in the referendum.
“I envision a party which will use the opportunity provided by Brexit to create jobs for working people, to protect our steel industry and manufacturing, to rebuild our fisheries and deregulate our small businesses. We will stand up for the working people who Labour ignore and the Conservatives despise. And we will be the party that stands up for our small businesses, helping them to create jobs and become the big businesses of tomorrow.
“We are not anti-immigrant or anti-immigration, but we are fiercely opposed to uncontrolled mass net immigration, which drives down wages and ultimately costs jobs.
“We’re finally moving power back from Brussels to Westminster, but now we must campaign further to devolve that power from Westminster to the people.
“I do not fear taking on the rudderless Labour Party in its heartlands. In my region, the North East of England, I led the Ukip fight at the 2015 General Election. We went from having below-average Ukip results in 2010 to gaining the highest Ujip share of the vote of any region in the country and we stand poised to gain Westminster seats.
“My two years as local elections coordinator, and six as the party’s general secretary, have given me an intimate understanding of the internal workings of Ukip and I propose constitutional reform that will achieve a dynamic, democratic party where the views of grassroots members and branches have greater input.
“Standing for leader has not been an easy decision for me to make, as I know the level of hard work and commitment that will be required. I have nothing but praise for the way that Nigel Farage, the greatest orator in modern politics, was able to devote so much time and energy to Ukip.”
Mr Arnott has been MEP for the North East since 2014. Prior to being elected he was the party’s general secretary for six years.
He enrolled at the University of Sheffield aged just 15, having gained his A-Levels three years early, leaving after having attained a Masters in Mathematics. He went on to become head of mathematics at a school in Sheffield before entering politics.