“I don’t know what it is to be British any more.” This from a man who is a professor at a prominent university and part of the British establishment. So how did it come to this?

For the past five years I have been interviewing the generation that came from the Indian subcontinent to postwar Britain. These early pioneers arrived with as little as £3 due to strict currency controls. They are now elderly people. I have watched as they have grown older, frailer, their voices weaker. Some have died. Their stories are an overlooked part of British history. It’s important to record them before it’s too late.

From 1948 until the early 1960s, these former subjects of the British Raj automatically became British citizens. They came here for a better life, and to rebuild the country after the second world war. Many worked the difficult shifts that no one else wanted – in the mills, factories, foundries and new public services. Many bore children here. Roots were laid ever deeper with each generation.

My BBC Radio 4 series Three Pounds in My Pocket has charted the social history of British south Asians from the 1950s onwards. The current series looks at the 1980s. The decade saw a new kind of Britishness expressed by the second generation, alongside concerns over integration. And dramatic events – such as the publication of The Satanic Verses and the Indian army’s storming of the Golden Temple in Amritsar, the holiest shrine for Sikhs – saw the British south Asian community start to fragment, largely along religious lines.

In the final programme I unpack the “Asian” part of British south Asian, and explain why it’s often difficult to give a succinct answer to that loaded question: Where are you from? You may have moved from one country to another during the partition of British India. You may identify with a region more than a country – say Punjab, Sylhet, Mirpur or Gujarat. Or the country you were born in may have become a new country twice over.

But what I was not expecting was for some interviewees to find the “British” part of British south Asian harder to define in the current political environment.

Runi Sayeed came to Britain in 1968 from Dhaka in what would become Bangladesh. She was a teacher. Recently, she’d got off the bus with her husband, and was walking down the street when a passer-by shouted at her: “Why don’t you go back to your country? Why are you here?”

Sayeed’s daughter Farah was furious. “She’s lived 50 years of her life here and only 24 of them in Bangladesh. So being made to feel acutely foreign again feels unacceptable. But it seems to be what’s happening.” When Farah says “again”, she means the outward racism she and her mother experienced almost daily in the 1970s and early 1980s. Farah feels the racist attitudes she thought had subsided, or at least were no longer voiced, are resurfacing in the public realm. And it started for them after the Brexit vote.

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Research suggests there was a rise in racially motivated hate crimes after the 2016 referendum. While exact demographic breakdowns aren’t available, a significant minority of British south Asians voted for Brexit. But almost everyone I spoke to for the series felt it represented a turning of the tide.

Amandeep Madra, who works for a global pharmaceutical company, says it’s not just post-Brexit. Donald Trump telling congresswomen to “go home” resonated strongly with him. It “was what you saw daubed on a wall or what you heard being screamed at you”, he says. And you can joke that home is Southall or Northolt, “but it still cuts really deep”.

The professor who told me he no longer knew what it was to be British is Gurhurpal Singh. He is a gentle, thoughtful man. He dislikes talking about the personal and prefers to speak as an academic, referencing data and evidence. So I was taken aback by his candour. He has spent nearly all his life in Britain. He came with his parents as a young boy from the Indian Punjab in 1964. He grew up in Leicester when to have a different skin colour invited trouble. He suffered physical attacks and saw the National Front marching in the street. Yet he says since the referendum he feels more rootless than ever.

Over his lifetime there was progress. Laws criminalising racism were enacted, minority political representation increased and cultural expression grew. He thought things could only improve, that it was a one-way road. He now feels that was just a theory “sold by liberals to migrants who came here … And it’s been proven that radical reversals occur.”

Five years ago when I embarked upon recording testimonies of those who came to Britain so many decades back, I did not expect to hear them talk like this. The things Singh said saddened me. He has spent nearly all his life in this country – making significant contributions – and he says he now no longer knows how to relate to contemporary Britain.

The political climate has changed towards minorities – it’s not only Brexit, or Trump’s rhetoric. Racism became a central election issue. The two main political parties stand accused of antisemitism and Islamophobia. The Windrush scandal showed that, however long the first generation are here, you could still be sent back. People from ethnic minorities feel this all acutely, even if they have been here for decades. They are all the “other”. They have heard these racial slurs before, recognise this hostility. They just didn’t think they would have to live through it all again.

• Kavita Puri is the presenter of the Radio 4 series Three Pounds in My Pocket. The final episode is on Radio 4 today at 11am