Boris Johnson has warned any further delay to Brexit will spell disaster for the Conservatives ahead of the launch of his leadership campaign.
He will tell supporters the UK must leave on 31 October and any more “can-kicking” will mean defeat for the party at the next general election.
He will say his two election victories as London mayor mark him out as the person most able to beat Jeremy Corbyn.
Home Secretary Sajid Javid will also make his pitch to MPs on Wednesday.
In a campaign video released on Tuesday, Mr Javid said he would bring a “fresh look” to the Conservative Party and was capable of healing the divisions caused by Brexit.