Labour’s governing national executive committee (NEC) has turned down a request from party members in Newham for an inquiry into how Sir Robin Wales was chosen to seek election as the borough’s mayor for a fifth time next year despite two of the organisations that supported him conducting their own investigations into how their votes were cast, one of which has concluded that its local branch broke its own rules.

Sir Robin announced his re-selection, secured by 20 votes to 17, to a full meeting of Newham Council on Monday. The NEC had concluded on 24 January that the result of the close-run local “trigger ballot” to decide if he would automatically become Labour’s candidate for May 2018 or face challenges from other hopefuls should stand.

However, the national Fabian Society has informed its Newham branch, which is affiliated to Labour locally and voted “yes” to Sir Robin’s automatic re-selection, that it had “breached the society’s rules” for determining how trigger ballot votes should be cast and that “the Labour Party has been informed” of the outcome of its review of what occurred.

In a 13-page letter sent to the NEC prior to its meeting last week, 47 Labour members in Newham, including ten councillors, asked that the Fabians’ vote “be held in abeyance and not counted” on grounds that included failure by local officers to hold a meeting of members to discuss which way their “trigger ballot” vote should be cast. A statement from the national Fabians said, while it accepted that its Newham officers had acted in good faith, “the national society’s by-laws require a vote of members in the re-selection of a mayoral candidate” and that this had not taken place.

Separately, one of the trade unions whose vote helped Sir Robin to victory is looking into whether the locally-affiliated branch responsible for the decision followed the correct procedures. Gerry Morrissey, general secretary of media union BECTU, has told On London that, although the union’s head office had no involvement in the matter, the way the “yes” vote was settled is to be considered by its executive committee later this month. BECTU has recently become a sector of another union, Prospect, and dis-affiliated from Labour with effect from 1 January.

The letter from the Newham members to the NEC stated that the signatories “do not believe” that local affiliation fees to East Ham constituency Labour Party (CLP) had been paid by the BECTU branch and that “a communication” from the union’s branch delegate suggests that the person concerned decided how to vote in the ballot without any consultation with fellow BECTU branch members. In this case, they asked that the ballot “be declared void and that BECTU be deemed not to have voted”.

It was among a large number of points made about the trigger ballot process as a whole in a sometimes the strongly-worded document, which asked the NEC to void or hold in abeyance a total of seven of the 20 individual “yes” votes, comprising two from unions, two from other affiliates and three from party ward branches, of which two took the “yes” option by a single vote. Eleven out of 20 ward branches voted “no” to the automatic re-selection of Sir Robin.

The letter also asked the NEC to examine why some eligible unions cast more than one vote and suggests that inconsistent interpretation of the rules arose from a major failing in the running of the trigger ballot process. The GMB cast four votes (all “yes”), the CWU cast three (two “yes”, one “no”) and Unite cast two (all “no”) while Unison (“no”), Usdaw (“yes”), the TSSA (“yes”) and Bectu (“yes”) cast only one each. The letter attributes this to some locally-affiliated union branches each casting individual and other unions only voting once no matter many branches had affiliated locally to one of the two Newham CLPs as a result of rules being interpreted differently.

The CWU and TSSA have not responded to email requests to comment on the matter and the GMB, despite several requests and an assurance that a response would be provided, have yet to offer answers to any of the questions first put to them about the trigger ballot process before Christmas.

In email correspondence Newham party members, Labour Party general secretary Iain McNicol has written that the trigger ballot was “raised very briefly” at the NEC meeting and that “there was a short discussion” but that the body “did not discuss or agree to pausing or changing the result of this process”. He added that “NEC members have agreed to come to Newham and speak to members about what lessons can be learned from this process [regarding] how future trigger ballot processes can be conducted in a way that best engages members and affiliates”. It is believed that two NEC members will be involved. Signatories to the letter are considering how to respond. One has expressed dissatisfaction to McNicol that the request for an inquiry has not been granted.

In a statement, Labour’s London region has said that, “the process in Newham was carried out in line with established rules and procedures”. A source close to Sir Robin has denied that the ballot process was flawed and suggested that an influx of new members prompted to join the party since May 2015 in order to support Jeremy Corbyn, Labour’s leader, lies behind much of the opposition to Sir Robin, although only members who joined before 25 April 2016 were entitled to vote in their ward ballots to determine which way to vote in the trigger ballot, which ran from 25 October until 4 December. This would have excluded any Newham members who joined Labour last summer in order to help Corbyn defeat the challenge to his leadership by Owen Smith.

The source also contends that a group of local Labour members called Trigger Democracy, which has campaigned for an open selection, is a manifestation of this, something the group itself denies, saying its members “aren’t anti-Robin” and “don’t represent any faction”. Those behind it decline to reveal their names on the grounds that they “wanted to provide as neutral a platform as possible” and because some of them work in or for the borough.

Newham is notable for all 60 of its councillors being Labour. Some of these and other local members believe that Sir Robin has been in the job too long and that his grip on the machinery of the Town Hall has made it difficult to hold him to account. Even so, the letter to the NEC said that its signatories would support his candidacy without equivocation if they considered it secured “as a result of an open and fair re-selection process”.