More than five million voters will receive the leaflet, which carries pictures of the two Tory heavyweights and statements on Europe from each. It asks bluntly: "Are you more a Clarke Conservative than a Hague Conservative?"
The politically explosive move, by the breakaway Pro-Euro Conservative Party, comes as Mr Hague's position as leader appears increasingly shaky.
Sharp divisions among the Shadow Cabinet emerged last week following the announcement of plans - on the night of a dinner to celebrate the 20th anniversary of Baroness Thatcher's election as prime minister - to abandon the Tories' free-market approach to the welfare state. She has reportedly "gone ballistic".
Yesterday John Major came under pressure to abandon his safe Huntingdon seat for Chris Patten, the former governor of Hong Kong, who has been tipped as another candidate to lead the Tories.
The anti-Hague leaflet, which places Mr Clarke at the forefront of a potential leadership bid, is designed to shore up a protest vote against the Tory leader in June's elections to the European Parliament. The authors, two Euro MPs who resigned the Tory whip last year in protest at his decision to rule out British entry into the single currency for the time being, hope that a poor showing in the polls will bring about a challenge for the leadership.
"In a whole range of respects Clarke is a much better leader than Hague," said John Stevens, one of the leaflet's authors.Reuse content