The senior Labour politician and former deputy leader Roy Hattersley has written to Jeremy Corbyn asking him to intervene to stop one of his most loyal supporters campaigning for the deselection of centrist MPs, saying such tactics risked leading to a repeat of the party split of the 1980s.

Hattersley, who was in the Commons for 33 years and Labour’s deputy leader for nine , said in his letter to Corbyn that the efforts by Chris Williamson, the MP for Derby North, would alienate floating voters and risked causing a split in the party.

Williamson, an ardent Corbyn supporter who has previously suggested Labour MPs critical of the leader should lose their seats, is on a speaking tour arguing for mandatory reselection for MPs, with critics saying it is focused on areas represented by moderate members.

In his letter to Corbyn, Hattersley said he attended one of the Democracy Roadshow events last week in the South Yorkshire constituency of Penistone and Stocksbridge, where the local MP is Angela Smith, a regular critic of Corbyn.

Hattersley, who has condemned Corbyn in the past, said Williamson’s speech had an emphasis on mandatory reselection for MPs.

He wrote: “I do not question the right of a constituency Labour party to replace a sitting member with a new candidate. What is intolerable is a campaign to promote indiscriminate reselection which is organised from outside the constituency, supported by new recruits who have been briefly enrolled for that purpose and is intended to benefit candidates of a particular point of view.”

Hattersley, who was made a peer in 1997, continued: “A reselection campaign, whatever its outcome, will alienate floating voters whose support we need. Were it to have any success, the consequences would be catastrophic.

“Reselection and the prospect of reselection will undoubtedly split the party – led not just by sitting MPs who were deselected or feared deselection but also by MPs who think that the attempted cull of their colleagues demonstrated that Labour no longer represented their view of the good society.

“I lived through the split of the 1980s and failed in my attempts to prevent it. To avoid a repetition of that disaster you must speak out against the narrow sectarianism that Christopher Williamson and the campaign for re-selection represents.”

The letter asked Corbyn to seek to persuade Williamson to end his campaign. The letter adds: “If he fails to respond to your request, I ask you publicly to make clear that, far from enjoying your support and approval, you regard his campaign as wrong in principle and deeply damaging to Labour’s prospects of election.”

Hattersley, who copied his letter to South Yorkshire Labour MPs and to the Sheffield-based former Labour cabinet minister David Blunkett, told the Guardian the leadership was “betraying the people the party was created to serve”.

He said: “Faced with the most incompetent government this century, it should be 20 points ahead on the opinion polls. But because of a combination of its own incompetence and its enthusiasm for ideological claptrap, it is squandering its chance of winning the next election. It has to change or it will become a political irrelevance.”

In response, Williamson said the Democracy Roadshow “has never asked Jeremy Corbyn for his endorsement, nor has he given it”.

He said: “The Democracy Roadshow is a grassroots initiative discussing the ongoing Labour party democracy review and campaigning for the open selection of MPs, which is commonplace in other democracies around the world. We’re visiting any group of party activists that invite us, and the response has been overwhelmingly popular.”