Sir Keir Starmer, the favourite to succeed Jeremy Corbyn as Labour leader, has called for the party to become a “trusted force for good” as up to nine rival candidates consider whether to stand next week.

The shadow Brexit secretary is seen as the candidate to beat following a YouGov poll showing he has a commanding lead over nearest rival and Corbyn ally Rebecca Long-Bailey, the shadow business secretary.

Commissioned by the Economic and Social Research Council’s party members project, the poll asked Labour members to list likely contenders on order of preference, with 31% opting for Starmer, 20% for Long-Bailey, and 11% listing Birmingham Yardley MP Jess Phillips as their first choice.

In his first comments since the release of the poll, Starmer refused to officially confirm that he would stand, instead telling Sky News: “The most important thing is that the Labour party is rebuilt, we learn the lessons of the last general election, reflect on them, and address them. But we need the Labour party as a trusted force for good.”

The poll’s findings, which did not include either affiliated or registered supporters, have prompted some concern among MPs and members who believe Starmer, the member for Holborn and St Pancras, is the wrong candidate to win over seats in the Midlands and the North that were lost to the Tories in the general election.

Neil Coyle, MP for Bermondsey and Old Southwark and a supporter of Phillips, said “another white bloke from Islington” was not going to win back Labour’s lost heartlands.

Long-Bailey, the MP for Salford and Eccles, has been seen as the candidate to continue Corbyn’s transformation of the party. Ian Lavery, Labour’s chairman, said that he is still considering his options despite speculation that he may drop out to ensure that Long-Bailey has a smooth path. A spokesman said Lavery has been “inundated with requests from Labour members and supporters asking him to stand”.

Lisa Nandy, the MP for Wigan is expected to make a decision this weekend after being urged to stand by union and party members. The only candidates to declare so far are the shadow foreign secretary Emily Thornberry and the shadow treasury minister Clive Lewis.

Yvette Cooper, the former welfare secretary who has long been touted as a possible leadership candidate, is expected to rule herself out of the contest. A friend told the Guardian: “The party membership is currently looking for someone who has been in Jeremy’s shadow cabinet not someone who has been in the actual cabinet under Gordon Brown.”

Others considering whether to stand include David Lammy, the Labour member for Tottenham, and Dan Jarvis, the Sheffield City mayor.

The contest has to take at least five weeks, according to party rules, but the actual timetable will be decided by a meeting of the party’s national executive committee on 6 January.

Some on the left of the party have grown increasingly concerned that Starmer could be buoyed by a “centrist insurgence” of registered supporters – members who pay a one-off fee to vote in the leadership contest.

A party source said that members of the party’s ruling body which is dominated by Corbyn supporters are being asked to open registration for a limited period.

“There is real concern that there could be an influx of people who don’t share the party’s values,” the source said.

Under Labour’s preferential voting system other candidates would be successively knocked out.

The YouGov poll does not include affiliates such as trade unions and registered supporters, who have also been able to vote in previous elections. Exact rules for this contest are still being finalised.