Tristram Hunt, the shadow education secretary and leading Labour moderniser, has rejected talk of a split in the Labour party, or legal challenges to the outcome, if Jeremy Corbyn is elected leader – warning that anyone who plans to quit will only be playing into the hands of the Conservatives.

In a speech to the Progress conference in Birmingham, he warned the modernisers were in danger of becoming a spent force in the party, and must do more to rebuild their strength.

Hunt said: “Forget talk of splits. I have no patience with anyone muttering now about breakaways or legal challenges or changing the rules to keep people out. They are playing into the hands of the Tories.

We have a Blair complex, we need to get over him and it. We cannot define ourselves against a figure from our past

“Whoever is elected as the new Labour leader ... I will continue to serve our party, seeking to hold this government to account and to develop the ideas, policies and campaigns that we need to become a government ourselves once more.”

He has not changed his mind since he previously said he would not serve in a Corbyn shadow cabinet, arguing there were other valid ways to serve the Labour party. One of the great unresolved issues is the extent to which Corbyn, by modifying his policies, can attract mainstream MPs on to his front bench. He has backtracked on a series of issues in a bid to avoid an immediate confrontation.

Hunt, who had wanted to stand in the leadership contest but was unable to muster the support among fellow MPs, criticises the way party modernisers conducted their campaign on behalf of their favoured candidate, Liz Kendall. It is widely expected that Kendall will come fourth after a bright start in the ballot when the result is announced on Saturday 12 September.

He warned: “Those of us who advocate modernisation risk becoming a spent force in the debate about the future of the Labour party. In the current leadership election, we focused too much on restoring policies from the 1990s rather than a programme for the 2020s focused on the way the world is now.

Hunt has said he will not be part of a possible Jeremy Corbyn-led shadow cabinet. Photograph: Justin Tallis/AFP/Getty Images

“And, instead of embracing rule changes which can open our party out to the rest of the country, we became inward-looking. As a general rule, if you are losing elections, it is not a good idea to complain that too many people are voting. The solution is to go out and win some more votes”.

He urged the whole party to get over its complex about Tony Blair: “If we are honest with ourselves, the last two leadership transitions have been about positioning the party against Tony Blair – both Gordon Brown and Ed Miliband sought, to a greater or lesser extent, to position themselves against Blair. Jeremy Corbyn’s campaign playbook contains a more extreme narrative about his opposition to Blair’s legacy.

“Where does this stop? The public will be confused as to why a politician elected to the leadership more than 20 years ago continues to occupy the minds and dominate the thinking of today’s leadership ranks within the Labour party. We have a Blair complex, we need to get over him and it. We cannot constantly define ourselves against a figure from our past.”

At the same event, Pat McFadden, the shadow Europe minister, criticised Corbyn for refusing to be clear whether he was willing to see the UK to leave the EU.

He said: “Three candidates have said unequivocally that they will campaign for Britain to stay in the EU, but the favourite, Jeremy Corbyn, has fudged. Asked to state his view, beyond the rhetoric there is no clear answer. Yet those who seek the mantle of leadership have to exercise leadership.

“Whatever changes the Electoral Commission has recommended to the wording of the question, the word “maybe” is not going to be on the ballot paper. To lead is to choose and all the speeches in the world about a workers’ Europe will not absolve anyone of the responsibility of answering the basic question of whether Britain should be in or out. This cannot be ducked because the country’s economic future, how we see ourselves and how we see the rest of the world depend on it.”