The Conservative backbencher John Bercow has stepped up his campaign to replace Michael Martin as Speaker of the House of Commons, emailing all 646 MPs to ask for their support and outline his "vision for the role".

In a seven-page document, Mr Bercow sets out his credentials, saying: "I have a track record of political independence, pursue unfashionable but important causes on a non-partisan basis, and can demonstrate competence in chairing and communicating."

Mr Bercow goes on to explain that the next Speaker "faces an unprecedented challenge... to clean up politics". He addresses the expenses scandal with the insistence that Parliament should "accept external advice on a new allowances system"; advocates an "enhanced scrutiny both of policy and of legislation" by backbenchers; and says that the role of Speaker should be one of an "ambassador" – "both a speaker and a listener".

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After two Labour Speakers, it is thought that the next Speaker will be a Tory, but while Mr Bercow has wide support among Labour MPs, he is unpopular within his own party. Michael Martin will leave his post on 21 June and his replacement will be chosen in a secret ballot the next day.