The six contenders vying to become Britain's next prime minister held a leadership hustings on Saturday with rival candidates aiming their fire at frontrunner Boris Johnson.

The men battling for the leadership of the governing centre-right Conservative Party spoke at a central London hotel ahead of a week of voting that will whittle them down to two.

The contenders were warming up their arguments ahead of a 90-minute televised debate on Sunday although Johnson is sitting it out, claiming direct bickering between them will be counter-productive.

Johnson, who will be given an empty podium in the Channel 4 programme, will take part in a BBC debate on Tuesday.

Conservative MPs whittle the contenders down to two through successive rounds of voting before the 160,000 grassroots party members pick the winner in a postal ballot.

Speaking at the National Conservative Convention hustings meeting, Johnson said he wanted to revitalise the party.

"What we need to do is to speak with confidence again about our basic Conservative message," the former foreign secretary said, according to his campaign office.

"The basic idea that it is wealth creation, it is free market economics that is at the heart of delivering the revenues that we need to pay for civilised objectives."

He said he was the candidate that could win back voters who have drifted to the Brexit Party and the centrist Liberal Democrats, then beat the main opposition Labour Party.

He branded Labour leader Jeremy Corbyn a "high taxing, high spending, Hugo Chavez-admiring, anti-Semitism-condoning apologist for the Kremlin".

Johnson topped Thursday's first round with 114 votes, ahead of Foreign Secretary Jeremy Hunt on 43 and Environment Secretary Michael Gove on 37.

Former Brexit secretary Dominic Raab got 27, interior minister Sajid Javid got 23 and International Development Secretary Rory Stewart was on 19.

There are 50 votes to play for that went to candidates who have dropped out and contenders need 33 votes to get through Tuesday's second round, when at least one more candidate will be eliminated.

'BLUE ON BLUE' ATTACKS

A report in The Daily Telegraph newspaper report suggested senior party figures had drawn up plans whereby other candidates could pull out, leaving Johnson as the only person going to a confirmatory vote of the membership, in order to avoid weeks of damaging "blue on blue" attacks.

Speaking as he left the private hustings at the London hotel, Javid said: "I don't want to see a coronation. There needs to be a proper process that's followed through."

Stewart attacked Johnson for entering the event via a side door, thereby avoiding speaking to reporters. Former London mayor Johnson has faced criticism for giving few interviews and public appearances.

"The whole genius of British politics is that we don't behave like American presidents sweeping up in a motorcade. We're all about talking to people," Stewart said.

Raab had earlier launched a broadside at Johnson, saying the party did not need a leader who could be "easily caricatured as being from the privileged elite", and suggested he couldn't "take the heat" of the TV debates.

The winner of the members' vote will be announced in the week beginning July 22 and then take over from Theresa May as prime minister.