A Nationwide customer seeking election to the building society’s board has criticised the lender for “unfair” treatment and undermining democratic governance after it said it would tell members to vote against him.

James Sherwin-Smith said Nationwide had tilted the field against him after it confirmed it would give members a default “quick vote” option that included a vote against his candidacy at the annual meeting in July.

Nationwide, Britain’s largest building society, is mutually owned by its member-customers. The last member to sit on Nationwide’s board retired in 2002, but Sherwin-Smith has mounted a campaign to change that, arguing it would help improve accountability at the lender amid concerns members did not have enough say.

However, Nationwide’s chair, Kevin Parry, said in a statement on Thursday that “his election would not be in the best interests of the society” as Sherwin-Smith did not have the necessary experience. Nationwide has 17 million members and more than £377bn in assets.

Sherwin-Smith said: “They have skewed this massively against me and they’ve also attacked me on my suitability for the board.”

The quick vote option is presented to all Nationwide members as an easy way to go along with the board’s recommendations. Last year, 87% of about 670,000 votes cast used the quick-vote system, meaning Sherwin-Smith will face an uphill battle to inform members of the choice on offer.

He said the move to make a vote against him the default was a “dangerous precedent for mutuals and democratic governance”. The Labour MP Navendu Mishra last week criticised “emerging governance issues” across the building society sector.

Nationwide has also blocked Sherwin-Smith from making changes to election materials to try to inform members they should not use the quick vote if they wish him to join the board, he said.

Sherwin-Smith also sought to rebut Nationwide’s criticisms that he did not have relevant experience. He is a former executive at the payments company Vocalink and has worked as a management consultant at Oliver Wyman focused on retail banking.

In an update to his campaign, Sherwin-Smith wrote: “Boards benefit from diversity of perspective and thought, not simply similarity of background. Ultimately, I believe members should have the right to be represented by one of their own, who has been nominated and elected by them. I don’t believe it is right for an incumbent board to act in a way that entrenches their position and disadvantages a member-nominated candidate.”

Parry said: “No board, regardless of whether it is of a mutual or public company, should ever recommend the appointment of a director who does not have the skills and experience necessary to do the job.

“While our members will have the final decision in this election through the normal voting process used for all directors, Nationwide’s board could not recommend Mr Sherwin-Smith for election following its assessment.”