Black and ethnic minority voters are backing Jeremy Corbyn in far higher numbers than the overall electorate as the two main political parties vie for their votes in crucial swing seats.

Labour is leading the Conservatives by 25 points among black, Asian and minority ethnic voters (BAME), according to polling by Opinium. More than half (52%) said they could imagine Corbyn in Downing Street.

The figures have been disclosed as the two main parties make a concerted push to win over the BAME vote with specifically tailored policies. They appear to reinforce the belief that second- and third-generation BAME immigrants, alarmed by the Windrush scandal and allegations of Islamophobia within the Conservatives, still distrust the party.

Despite the latest data, the Conservatives believe they are gaining support in areas with large Hindu, Sikh and African communities, with promises of business-friendly policies and an easing of post-Brexit immigration restrictions on Commonwealth countries.

It came as the campaign group Operation Black Vote (OBV) said the BAME vote could dictate the outcome in 100 key marginals including Labour-held Kensington, Newcastle-under-Lyme, Richmond Park, Southampton Itchen, Peterborough and Portsmouth South.

Lord Woolley, the founder of OBV, said that during this election, the BAME vote will be more crucial than ever. “There have never been so many marginal seats, and there have never been so many where the BAME vote is important,” he said.

“The implications for people of colour are writ large in this election. The Brexit narrative says ‘we are a white, Christian nation and we are going to assert that’. Think about it and you begin to realise how important those votes will be.”

Opinium surveyed BAME voters nationwide between 5 and 14 November and discovered differing approval ratings from those in the electorate at large.

Nearly half of BAME voters (49%) said they intend to vote for Labour compared with 24% for the Conservatives. However, 38% believe they will not get their way and Johnson will be returned to Downing Street, compared with 23% who think that Corbyn will succeed on 12 December.

While Corbyn had a +8% rating when ethnic minority voters were asked about his handling of his current job, Johnson had a -22% rating. When a Delta poll of the whole electorate asked a similar question about whether the leaders were doing their jobs well, it delivered a -34% approval rating that Corbyn was compared with -10% for Johnson. The poll was conducted between 14 and 16 November.

The figures might offer some hope for the Tories, who have traditionally struggled with minority ethnic voters. In 2017, Labour enjoyed an enormous 34% lead over the Conservatives among minority ethnic voters, a surge that has not yet materialised, according to Opinium’s data.

Corbyn last week launched the party’s first race and faith manifesto in an effort to woo BAME voters. Policies included a new public body to oversee the legacy of colonialism, a race equality unit at the Treasury, a pledge to introduce more black teachers and reduced charges for Home Office documents and tests.

The policy announcement was overshadowed by the chief rabbi’s criticisms of Labour’s leadership for failing to tackle prejudice against another minority, the UK’s Jewish community. Labour is facing a formal antisemitism inquiry by the Equality and Human Rights Commission, and pollsters believe the party could pay an electoral price for the allegations which have dogged it for three and a half years.

The Conservatives have included policies in their manifesto that they believe will appeal to minority ethnic voters. They include pledges to invest £90m into the Youth Futures Foundation to improve employment outcomes for young people, mainly in urban areas.

There is also a pledge to support for a memorial recognising the contribution of the Windrush generation after the scandal that dogged the party in 2017.

Senior Tories, including the home secretary, Priti Patel, and the chancellor, Sajid Javid, have attempted to exploit resentment among BAME residents over the apparent ease with which “white Europeans” could bring over spouses compared with BAME people from African, Asian and Caribbean countries.

Others say that the apparent wooing of BAME people may well take a back seat towards the end of the campaign. The Conservatives have acknowledged they must win leave seats in the north and the Midlands, which have large white working-class communities.

Sunder Katwala, the director of the British Future thinktank, said the BAME vote gets more important at every election because the population is becoming increasingly diverse.

But he expects the campaign to increasingly focus upon the needs of predominantly white communities whose votes are required for a working Commons majority. “Leave voting towns are, in the main, a little older and whiter. We can expect that the battlegrounds will be slightly less diverse seats,” he said.

“When the Tories have won, they have concentrated on less diverse areas and they can do that again. But in the long term, their strategy will have to change to find a way of winning over a more diverse and fractured BAME community,” he said.

There has been a recognisable change in the way BAME communities vote, Katwala said. First-generation immigrants could not bring themselves to vote for the Conservatives because of the party’s past pandering to racist attitudes exemplified by Enoch Powell’s speeches and Norman Tebbit’s “cricket test”.

“Ask younger BAME people, they do not know who Enoch Powell is. His resonance is of less importance and other mainstream issues such as health, education and the economy are of more importance,” he said.

Politicians will continue to ingratiate themselves with ethnically diverse communities during election campaigns, Katwala said, but can no longer rely upon a bloc vote to turn out.

“It is fine if politicians go to gurdwaras and mosques as they always do for photo opportunities but they must drop the idea that ethnic minority voters turn up to those places to be told how to vote any more than a white British voter turns up to a C of E chapel to hear how they should vote,” he said.

