Labour has been warned it could be “going backwards on equality” by two senior MPs who expressed their alarm at the decision not to replace some departing female colleagues with all-women shortlists.

The concerns of Labour MPs Gloria De Piero and Harriet Harman follow criticism of the party’s procedures by the Unison general secretary, Dave Prentis, who accused the Labour leadership of “trading” seats intended for female candidates in order to allow “favourite sons” to take up the safest Labour seats.

De Piero, who has said she will step down as the MP for the hyper-marginal seat of Ashfield at the next election, said she was pleased her seat would be replaced with an all-women shortlist but said she was angered that was not the case in other seats.

The MP criticised the selection process in Stockport, where the Labour MP Ann Coffey defected and a male candidate was selected last week, and in Vauxhall where there will not be an all-women shortlist to replace the retiring Kate Hoey.

“There have always been circumstances where seats with a retiring woman can be designated open but following NEC designation in Stockport this looks like we are going backwards on equality,” she said.

Her concerns were echoed by Harman, who said the party’s national executive committee should explain its decision-making process. “Can we have a statement from NEC on this?” she tweeted.

“Policy is AWS [all-women shortlist] when replacing woman MP & 50% AWS in others till we achieve parity. Has the policy changed?”

In 10 seats where MPs have announced they are retiring, half have been allocated all-women shortlists, including seats like Poplar and Limehouse which has a male MP, Jim Fitzpatrick.

A Labour source said the party was still on course to reach 50-50 gender parity after the next election and that 72 women candidates had been selected out of 102 seats where selections had taken place so far.

All-women shortlists save Labour from near-total male domination Read more

A party spokesman said: “The Labour party has more women MPs than all other political parties combined, we are committed to improving diverse representation at all levels of the party.”

One seat which has been designated as an open selection is Vauxhall, the seat of Labour Brexiter Kate Hoey. The south London constituency is expected to be fiercely contested, including by two high-profile women, the former MP Katy Clark who is now Corbyn’s political secretary, and the lead organiser of Momentum Laura Parker.

In a statement on Twitter, Vauxhall CLP said: “We are extremely disappointed to learn this morning that the NEC has rejected our call for an all-women shortlist in selection of our next MP. Vauxhall members unanimously passed a motion last month making this request. We call on the NEC to respect the decision of local members.”

The statement demanded that a selection process be allowed to begin immediately, suggesting the party would not stand for a candidate being imposed – an implicit criticism of Hoey.

“The threat of an autumn general election grows larger daily as we head towards a dangerous no-deal Brexit, which no one voted for. And 79% of Vauxhall electors voted against Brexit,” the group said.

“We will not stand for a candidate to be imposed by backdoor means on the constituency if a snap election is called. In 1989 the local candidate Vauxhall members chose was denied to us, and we are determined this does not happen again.”

A senior NEC source said that it was largely still the case that all-women shortlists could be used to either block or promote a favoured candidate, but there was technically no rule to say that a seat with a departing female MP must be replaced by a woman.

“There have always been stitch-ups and this dates back to many previous Labour leaders but there is technically no policy in place even though we are increasing the number of all-women shortlists,” the source said.

The warnings came as four BAME groups associated with Labour raised concerns with the party on Tuesday about the number of ethnic minority candidates who had been selected – and suggested trade unions needed to do more to promote diverse candidates.

In a letter to the party, Chinese for Labour, Sikhs for Labour, Labour Friends of Somalia and Labour Black Network said the party should be prepared to select diverse candidates in regions which were traditionally white.

“Labour must be as comfortable selecting someone from Kurdish, Somali, Chinese, east European, Pakistani, Indian, or African heritage in Rother Valley and Blyth Valley as we are in Coventry or Ilford,” the letter said. “There should be no no-go areas for BAME candidates.”

All-ethnic minority shortlists are not legally permitted, but the groups said selection committees should be encouraged to make lists at least 50% BAME candidates to increase the likelihood of them being selected.

The letter also suggested that trade unions, who have significant influence in seat selections, should look critically at how few BAME candidates they had backed in the past and “recognise they have to play their part in redressing the balance”.

“It is unfortunately still the case that trade union supported candidates in selections are often white men and drawn from a narrow pool of individuals,” the letter said.

“This gives the impression of a closed shop of candidates supported by trade unions despite the shop-floor membership of those unions often being extremely diverse.”

A number of fierce selection battles are also expected in seats where Labour MPs defected to other parties or are sitting as independents. Chuka Umunna’s Streatham seat is likely to be contested by Diane Abbott’s chief of staff Bell Ribeiro-Addy and London Assembly member Florence Eshalomi.

Sam Tarry, a TSSA union official who was a key figure in Corbyn’s 2017 election campaign, has said he will fight for selection in Ilford South, the seat where Mike Gapes defected to the Independent Group for Change.