Mr Bolton refused to resign during a statement at 4pm this afternoon. It comes after ano-confidence motion by Ukip’s national executive committee (NEC).
He said he had lost confidence in the party’s ruling committee and said it was time to “drain the swamp”.
He called for unity within Ukip and among Leave supporters, saying Brexit should be everyone’s main focus.
Mr Bolton said: “During the next four weeks I shall be calling for the coordination and mobilisation of all Leave campaigns, to ensure that the government delivers full independence from the European Union in all areas of government and administration and I shall be calling for the Party itself to mobilise to support this agenda.
“This is the most pressing matter facing our country and I am determined not to allow the NEC to distract the Party away from participating forcefully in the Independence debate.”
He also lashed out at the NEC.
Mr Bolton said: “Without reflecting at all on its individual members, the NEC, as presently constituted, is unfit for purpose and has severely handicapped the Party’s progress and political delivery for some years, as all recent UKIP leaders will attest.
“It has not only lost the confidence of me as the Party leader in its ability to act objectively as the Party’s governing body, it has also lost the confidence of a large proportion of the membership.”
“The NEC requires significant and urgent reform. To that end, again during the coming weeks, I shall be proposing a new Party constitution, with a newly constituted and reformed NEC. Likewise, it is now time to put an end to the factional in-fighting within the Party and to remove those who have been a part of that.
“In a single Phrase, it is time to ‘Drain the Swamp’.
Let me re-iterate, the most pressing issue facing our country is to ensure that we gain full independence from the European Union; that we do not allow the government to betray the country by compromising that goal. That is the object to which I shall be directing all of my energies in the coming weeks.”
It comes after it was released his then-partner Jo Marney had sent racist messages about Meghan Markle.
Mr Bolton has faced a stream of calls to resign since the highly offensive messages were published.
And today resignation after resignation has further damaged his authority as Ukip leader.
Deputy leader Margot Parker, assistant deputy leader Mike Hooker, London spokesman Peter Whittle, immigration spokesman John Bickley, trade spokesman William Dartmouth, culture spokesman David Meacock, communities spokesman Tim Aker, Brexit spokesman Gerard Batten, sports spokesman Bill Etheridge, liabilities spokesman Star Anderson, work and pensions spokesman David Sprason and MEP Jonathan Arnott have stepped down.
Mr Hookem, who resigned on Friday but made the decision public on Monday, said the situation had become an “almost farcical scandal”.
He wrote in his resignation letter to Mr Bolton: “Ukip is now in the preposterous situation of the leader’s private life being of more interest than the party.”
Ms Marney has defended Mr Bolton by referring to the private life of former Ukip leader Nigel Farage.
She tweeted: “Nigel split up with 2 wives. Both had children. You’re suggesting that a leader should be forced to remain in a relationship he doesn’t want to be in? Has he no right to happiness?
“This isn’t America. He’s the politician not me. As it stands, we are not a couple in any case. Henry is probably the most qualified leader in Britain with a truly phenomenal CV.
“People split up with their wives every single day. UKIP is not a church it’s a political party.”
This is a developing story. More to follow…