Christian Wolmar, Labour’s candidate to face Zac Goldsmith in the Richmond Park byelection, has insisted it is right for the party to contest the seat.

Senior Labour MPs, including the shadow business secretary Clive Lewis, had called for Labour to stand aside and strike a deal with the Liberal Democrats, making it more likely that Goldsmith could be beaten.

But Wolmar, a transport expert and campaigner, who was selected to fight the seat on Saturday, said it would have been wrong for Labour not to offer a candidate.

“I’m very firm about this. I think we’re doing the right thing. This is not a time when Labour should abandon the field to a rightwing party and a slightly right-of-centre party. I think it’s very important that we give people the chance to vote. We are the anti-austerity party,” Wolmar said.

He added that he had made that argument at the constituency party’s selection meeting, where some reports suggested a number of people were keen not to run a candidate against the Lib Dems’ Sarah Olney.

Advocates of a “progressive alliance” between left-of-centre parties suggested Labour could have stood aside, perhaps in exchange for the Lib Dems not standing against the Labour MP Ruth Cadbury in the neighbouring Brentford and Isleworth seat at the next general election.

The Green party, which won 6% of the vote in the constituency in 2015, has decided not to field a candidate. Its co-leader Caroline Lucas warned of a “regressive alliance”, with Ukip backing Goldsmith.

At last year’s general election, Goldsmith, then the official Conservative candidate, won 58% of the vote, with the Lib Dems on 19% and Labour 12%.

Speaking to the Guardian, Wolmar also appeared to defy his party’s line on Brexit, saying he would not be willing to give Theresa May a “blank cheque” by voting to trigger article 50.

“I really think we should do everything to try to prevent what is a disaster for Britain and a disaster for the people we stand up for,” he said. “There’s the vote coming up over the enactment of article 50. I think personally I would vote against it.”

Without clear pledges from the prime minister about how she would conduct negotiations with the other 27 EU member states, Wolmar said MPs would not have enough information about the process they would be beginning by backing article 50. “We don’t know what it’s about. What would we be voting for?”

The government has said it will appeal against Thursday’s high court judgment. The ruling means May cannot trigger article 50 without giving parliament a say. If it were to lose the appeal in the supreme court, the government would bring a bill to both houses of parliament, the Brexit secretary, David Davis, has said.

As things stand, Wolmar said he would oppose such legislation, even if it were a simple bill authorising the government to invoke article 50. “How could one possibly support something that has no real meaning?” he asked. “You’re giving the government a blank cheque.”

Jeremy Corbyn was forced to clarify his position on Sunday after an interview with the Sunday Mirror suggested Labour might be willing to block article 50 if May did not sign up to his party’s demands on issues including workers’ rights.

There must be transparency and accountability on Brexit terms. We won't block Article 50 but will fight for a Brexit that works for Britain — Jeremy Corbyn MP (@jeremycorbyn) November 6, 2016

Wolmar, who lives in Corbyn’s Islington North constituency, backed him for the Labour leadership in 2015, but then had such serious doubts about the way Corbyn was running the party that he supported Owen Smith’s challenge over the summer. However, he said: “I now totally support Jeremy; we have got to all get together.”

The author of a number of transport books, Wolmar sought the Labour nomination for London mayor, but came fifth out of six candidates in the primary election last year with less than 6% of the vote.