Members of the Labour Party are seeking legal action to determine whether the process to choose their party’s Newham mayoral candidate for next year was run lawfully.

Solicitors acting on behalf of up to 30 claimants have threatened litigation against Labour unless a new “open selection” process is held or the result is investigated.

They also claim “inconsistently applied and explained procedural rules” took place and need to be probed.

All of the grounds have been rejected by the Labour Party.

The trigger ballots, officially called the affirmative nomination process, ended in December.

Voters had to choose “yes” to keep incumbent directly-elected mayor Sir Robin Wales – who has held power since 1995 in a Labour-dominated borough – or “no” for an open selection process so other candidates could stand.

Each of the 20 Labour electoral wards in the borough had a vote while another 17 came from trade unions and socialist societies, collectively known as affiliated organisations.

Sir Robin won despite 11 out of 20 Labour wards voting for open selection because 11 out of 17 of the affiliates voted yes to keep him, taking his total share of votes to 20 versus 17.

However in letters sent by Irvine Thanivi Natas (ITN) solicitors to GRM Law, the firm acting on Labour’s behalf, it is alleged procedural rules were “breached” as they were applied differently to different affiliated organisations without their full understanding of what the rules were.

This meant some trade unions with several branches voted more than once, while others with more than one branch believed they only had one vote.

The letters also state organisers were questioned about inconsistencies before the ballots finished while Labour’s governing body, the National Executive Committee (NEC), did not adequately explore subsequent allegations of wrong-doing.

Claimant David Gilles said: “Reluctantly we’re having to resort to legal action to get this vote re-run.”

A Newham Labour Party spokesman said: “Following a selection process at the end of 2016, Sir Robin Wales was officially confirmed as Labour’s candidate for mayor of Newham.”

A national Labour Party spokeswoman said established rules and procedures were followed.