The government has defended its decision to push ahead with an imminent deportation flight to Jamaica despite last-minute legal challenges by people due to be on board, and concerns that Windrush citizens could be among those removed.

More than 100 cross-party MPs and peers have signed a letter to Boris Johnson calling for the flight to be postponed pending recommendations from a review into Windrush, while Labour said there was a worry British nationals could be involved.

The letter also cited concerns about the potential deportees’ access to legal advice and mobile phones, and how many had been in the UK since they were children.

But asked about the flight, due to leave on Tuesday – only the second the Home Office has chartered to Jamaica since the Windrush scandal – Rishi Sunak, the chief secretary to the Treasury, said: “All due process will have been followed.”

Q&A What is the Windrush deportation crisis? Show Hide Who are the Windrush generation? They are people who arrived in the UK after the second world war from Caribbean countries at the invitation of the British government. The first group arrived on the ship MV Empire Windrush in June 1948. What happened to them? An estimated 50,000 people faced the risk of deportation if they had never formalised their residency status and did not have the required documentation to prove it. Why now? It stems from a policy, set out by Theresa May when she was home secretary, to make the UK 'a really hostile environment for illegal immigrants'. It requires employers, NHS staff, private landlords and other bodies to demand evidence of people’s citizenship or immigration status. Why do they not have the correct paperwork and status? Some children, often travelling on their parents’ passports, were never formally naturalised and many moved to the UK before the countries in which they were born became independent, so they assumed they were British. In some cases, they did not apply for passports. The Home Office did not keep a record of people entering the country and granted leave to remain, which was conferred on anyone living continuously in the country since before 1 January 1973. What did the government try and do to resolve the problem? A Home Office team was set up to ensure Commonwealth-born long-term UK residents would no longer find themselves classified as being in the UK illegally. But a month after one minister promised the cases would be resolved within two weeks, many remained destitute. In November 2018 home secretary Sajid Javid revealed that at least 11 Britons who had been wrongly deported had died. In April 2019 the government agreed to pay up to £200m in compensation. Photograph: Douglas Miller/Hulton Archive

He told Sky News: “The people on this plane are people who have committed very serious crimes, whether it’s rape, manslaughter, murder.

“These are serious offences and we have a established process for ensuring that where we have foreign nationals who have committed crimes here, they should be, where possible, deported. That’s something that’s sensible and proportionate.”

Not all those on the flight have committed such serious crimes. Many have committed just one offence, in many cases drug supply, GBH or joint-enterprise crimes.

Speaking later to Sky the Labour MP David Lammy said he knew of eight deportees convicted of non-violent offences, and nine of drug offences.

Asked about Sunak’s comments, Lammy said: “It’s outrageous, because that’s what they said about the 164 people that they sent back to Jamaica [under Windrush]. And some of them died in the streets of Jamaica. And some of them were British.

“They are depriving 41 children of their parents. Many of these young men have children What will happen to them?”

Lammy also argued for an deportation flights to be halted in the run-up to the review into Windrush, conduced by Wendy Williams, an inspector of constabulary: “The right thing to do is to wait for their own review, where a leak last week suggests that Wendy Williams was saying: ‘Don’t deport people who who arrived here under 13.’ I think that sounds right.”

Diane Abbott, the shadow home secretary, said, “No one argues we should go soft on serious criminals. Labour has lambasted Tory governments for overseeing a surge in serious violent crime.

“The issue is whether all of these people are in fact foreign nationals, or some are actually British. We must not continue the Windrush scandal of deporting our own citizens.”

The Guardian spoke to 13 of those due to be on board the flight. They said between them they would be leaving behind dozens of young children, along with their immediate and extended families, if the deportations go ahead, and they would be putting their lives at risk because of gang violence on the island. Many have lived in the UK since childhood.

One of those involved, Tajay Thomson, arrived in the UK in 2001 aged five. Now 23, he has a conviction for a drugs offence for which he served a seven-month sentence in 2015. “I feel like my life has been taken away by the Home Office,” he said.

Asked if Thomson’s deportation was proportionate, Sunak said: “I can’t comment on the individual cases but I can tell you about the process, and of course due process will have been followed in matters such as these.”