Sir Marcus, a doughty Yorkshireman, beat off a challenge last year by Sir Nicholas Bonsor, who later was promoted to the ministerial ranks by John Major.
Mr Dunn's challenge marks the beginning of a wholesale clear-out of many of the leading backbench Conservative MPs from the 18-strong executive of the 1922 Committee and its officers.
The changes are being brought about because many of the MPs are standing down at the next general election. Mr Dunn regards his challenge as a move to ensure continuity, rather than a right-wing coup for the leadership.
A former education minister, Mr Dunn is a leading member of the 92 Group of Tory MPs, a powerful right-wing grouping run by Sir George Gardiner, which commands most of the key backbench committee posts.
He has the strong support of the 92 Group, and could unseat Sir Marcus from the chairmanship, if the MP for Shipley does not stand down. Sir Marcus is well-liked, but has been accused of being too close to the party leadership.
Among the leading members of the 1922 executive who have announced they are standing down at the next election are Dame Jill Knight, Sir Anthony Grant, Sir Anthony Durant, Sir Peter Hordern, and Sir John Hannam.
It could leave the way open for a younger generation of right-wing Tory MPs to represent the Tory backbench. Many backbenchers complained that the 1922 Committee executive failed to represent their dissatisfaction over policy to the Tory leadership and, instead, was used by the leadership to demand unity behind John Major from the backbench.
Sir Marcus was heavily criticised by those who thought he had gone too far in pledging the support of the 1922 Committee executive for Mr Major in the July leadership election. David Evans and John Townend gave their support to the right-wing challenger, John Redwood.
The outcome of the leadership election has settled Mr Major's position, but the changes likely on the 1922 Committee executive - in effect the shop stewards for the Tory backbench MPs - will guarantee that his leadership is left in no doubt that the backbenches want a hard-hitting manifesto for the election. They will also urge Michael Heseltine, the Deputy Prime Minister, to lead a more vigorous fight back by senior Cabinet ministers against Tony Blair's appeal.Reuse content