She said it was treating its first test at the ballot box "very, very seriously indeed", as the campaign itself would "send the loudest possible message to both the government and the opposition about how people in the United Kingdom feel about leaving and the deal that is now on the table".
He said: "I hope she does accept the fact the call for her resignation now is growing into a clamour".
Nigel Farage with the candidates unveiled at the Brexit party press conference on Tuesday.
"Instead we must offer a radical alternative based on our values that speaks directly to the people we represent and demonstrate Labour has a way forward out of the crisis".
Ipswich Conservative Chairman John Howard has joined calls for Theresa May to step down as Prime Minister.
She described the candidates as from "every corner of the UK" and from "all walks of life".
Unlike May, Corbyn seems in no hurry to get Brexit done, people familiar with the matter said.
Ministers are wary of putting the bill before MPs unless they are confident of getting it safely through the Commons.
"I'm sure that Boris understands why this is not a vote against Boris", she said.
Dinah Glover, chairwoman of the London East Area Conservatives, said there was "despair in the party". No date has been announced for the vote, in which the party's 800 highest-ranking officers will take part.
On Monday, it emerged the PM could face an unprecedented vote of confidence in her leadership after 70 local Conservative association chiefs signed a petition in support of a poll.
Some Conservative lawmakers are discussing whether the rules could be changed to allow a new vote on May's leadership.
They are preparing for the vote as the latest Brexit delay means the United Kingdom may have to take part.
Britain is set to take part in the European Parliament elections on May 23 because it has not left the EU, nearly three years after voters backed Brexit in a referendum.
The next leader will be chosen by a vote of all Tory members from a shortlist of two selected by the party's MPs.
May's allies fear that a victory for the euro-skeptic Farage will push many moderate Conservatives into adopting a more hard-line stance.