David Cameron is under pressure to rip up the rulebook for choosing Conservative parliamentary candidates after a series of bitter rows with grassroots activists.

Party members are preparing to meet in emergency session tonight to decide whether to deselect Liz Truss as candidate for the safe seat of South West Norfolk.

Her traditionalist opponents — branded the “Turnip Taleban” — are furious that she failed to disclose an affair with Mark Field, a married Tory MP, when she was chosen less than a month ago. Others resent the “dictatorial” way in which Mr Cameron has supported a candidate he regards as a model new Conservative.

A senior figure in Tory high command, however, conceded yesterday that the fight over Ms Truss was just one of more than half a dozen where the party had been “cack-handed” over recent selections.

There have been resignations and protests by local association officers over interference from party headquarters in almost every region of the country over the past year.

More are expected in January when Mr Cameron imposes “by-election rules”, including women-only shortlists modelled on those devised by Labour, to fill vacant seats after the parliamentary expenses scandal.

The source said: “When the election is over we are going to look at this entire system and acknowledge that mistakes have been made by trying to micromanage selections. A Conservative government is going to have enough problems with the membership on things like Europe without picking these fights.”

The Tory leadership has sought to change the male, middle-class face of the party by selecting more women and people from ethnic minorities and diverse social backgrounds.

Barely a fifth of the 507 parliamentary candidates selected so far are women and Mr Cameron has invested considerable political capital in ensuring that Ms Truss does not get hounded out of South West Norfolk. A vocal and socially conservative grassroots contingent is expected to defy him at tonight’s meeting in Swaffham. Even some of Ms Truss’s supporters believe that the selection process is flawed.

Hugh Colver, the local assocation’s deputy chairman, said: “We, as a party, need to look at the selection arrangements. If there’s a chance for candidates to be introduced by the constituents that would be a very good thing.”

Another senior figure in the South West Norfolk party said: “The selection process is rubbish, at best.”

He singled out for criticism Eric Pickles, John Maples and Shireen Ritchie, the leadership’s triumvirate who choose the long-list of about 150 candidates, summon the selection committee to London and advise on their shortlist.

“I lay the blame squarely at Central Office,” he said.

Mr Cameron’s advisers acknowledge that the difficulties are not caused solely by “neanderthal attitudes” among activists to selecting women or people from ethnic minorities. Instead, many appear to believe that interference from Conservative headquarters, including the introduction of primaries open to all voters, is robbing local associations of one of the few privileges they have as party members.

The rebellion is spreading across East Anglia with activists in Central Suffolk and North Ipswich also seething after being presented with a shortlist containing no local members — even though Tim Passmore, the council leader, was one of several who applied.

“It is a great disappointment to all who know Tim that his nomination has been rejected and six outsiders have been selected,” the Tory council group wrote in a letter of protest. “It can only be surmised that they represent David Cameron’s ‘gold list’.”

In Macclesfield two senior members of the Conservative Association have resigned in protest over the process that led to the selection of David Rutley, a former director at Asda, as successor to Sir Nicholas Winterton. Darryl Beckford, the association’s deputy treasurer, and Andy Lea, the treasurer, have quit, complaining about pressure from Mr Pickles, the party’s national chairman.

In Penrith and the Border, a prominent local Tory is demanding a review of the selection of Rory Stewart, a Harvard professor and former diplomat who was picked from another shortlist of outsiders last month.

“They [Mr Stewart and Mr Cameron] were peas out of the same pod — totally unrepresentative of people in the constituency,” John Stanyer said.

He added: “How can a man like him — Eton-educated — comprehend what it’s like to live here?”

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