A total of four candidates are to fight to succeed Roger Knapman as leader of the UK Independence Party.
Roger Knapman is stepping down as UKIP leader
Nigel Farage, leader of UKIP's MEPs, is the favourite to take over. The result of the vote is due on 12 September.
His rivals include party chairman David Campbell Bannerman, chairman of UKIP Wales Richard Suchorzewski and David Noakes.
There will be hustings between the candidates later this month before ballot papers are sent out in August.
The UK Independent Party's best known policy is a pledge to withdraw the UK from the European Union if it is elected to power.
It has never had anyone elected to the House of Commons, but had 12 Euro MPs elected when it finished third in the last European Parliament elections, with 16% of all votes.