Raheem Kassam has dropped out of the race to become the next leader of Ukip after citing concerns over the "integrity" of the process.

The 30-year-old journalist, who ran under the Donald Trump-inspired slogan "Make Ukip Great Again", has instead urged his followers to back candidate Peter Whittle.

Kassam's announcement comes just three days after he officially launched his campaign in a Westminster pub.

He portrayed himself as a "Farage-ist" candidate and pledged to increase Ukip's membership to more than 100,000.

He said his decision to suspend his leadership bid was prompted in part by senior figures within the party treating the leadership contest "like a coronation".

He said: "It is a decision I have not taken lightly, but following meetings this weekend I realised the path to victory is too narrow."

He added: "I am not satisfied about the integrity of the process, and having put a number of complaints in to the party chairman, I was disappointed that incidents whereby Members of the European Parliament are using party databases to effectively campaign against me – ostensibly against the rules – were not challenged."

Kassam, the former chief aide to Nigel Farage, also complained of "disgraceful" treatment by the media, citing an incident in which journalists allegedly turned up at his parents' house at dusk.

He said his campaign also suffered a lack of donations, failing to raise enough money to allow him to travel around the country to speak to supporters.

He added: "I wish the UK Independence Party and whoever its new leader is all the best in ensuring Brexit happens, and in the upcoming electoral tests next year. I remain committed to the causes of the UK Independence Party, but sadly, at this campaign, it was a bridge too far for us."

He said he is to continue in his role as editor-in-chief of right-wing news site Breitbart London.

Kassam's withdrawal means there are four candidates left in the Ukip race: Suzanne Evans, Paul Nuttall, John Rees Evans and Peter Whittle.

Nominations close on Monday, with the result to be announced 28 November.