By dint of my habitual forgetfulness I am an expert at breaking into my own house. Recently I sampled the more rarefied pursuit of trying to break back into my own country and found it rather more difficult.

It came about because in 2011, in Nad-e Ali, Helmand, I had the pleasure of making the acquaintance of an interpreter named Khushal. At the time I was serving as an officer in the British army and Khushal, appropriately nicknamed Happy, was a pleasure to work with. He got on well with the locals. He got on well with me and the team. Hardworking, unselfconsciously bright and habitually courageous, he had been interpreting for the International Security Assistance Force (Isaf) for two years by the time we met, which meant that he had a lot more experience of life at the sharp end of an insurgency than did I or many of the other soldiers.

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On patrol one day he alerted me to some odd movement up ahead which led us to change course … only slightly, but enough to narrowly avoid being in the blast of a command-operated improvised explosive device that had been laid in our path. I will never know with certainty if that bomb would otherwise have killed me. But I do know that Khushal, just like the soldiers I was with that day, was willing to lay down his own life for his friends – which is exactly what he considered us.

For friendship’s sake, on my return home, I kept in touch with him. When Cameron announced that he was going to relocate only those combat interpreters on our books in December 2012, I was disappointed – Khushal had left the job just a couple of months before. This week there were reports of an interpreter, known as “Popal”, who was denied refuge in the UK, being murdered by the Taliban and the head of the defence select committee has said that the government must “urgently” offer sanctuary to Afghan interpreters at risk in their home country.

As with other interpreters, Khushal’s talent began to cost him dearly. During his career with the British he had been picked to augment a special forces operation short on interpreters, and accordingly asked to carry a weapon. Word of this got out to the Taliban, who singled him out for particular persecution.

Having grown up in what had become undisputedly Taliban territory, their threats made it impossible for him to return home. The insurgents demanded his family reveal his location and when his older brother was tragically caught sending him messages, he was promptly executed. Khushal’s mother blamed him for the death and has not spoken to her son since.

Hanging around jobless in Kabul, Khushal still routinely bumped into people visiting the capital from his village and consequently felt continuously vulnerable. He had little option but to apply for help from the UK government under the scheme that had been set up precisely for people in his position.

But a year and a number of supporting emails from myself later and Khushal was still in limbo. It seemed the main hold up was the fact that his home area was too dangerous for those fact-checking his application to visit – a catch-22 situation not unusual for interpreters applying for UK visas and quite rightly labelled “Kafkaesque” by Lord Ashdown.

Eventually one of the Afghans working for Khushal’s arbiters warned him that no decision would realistically be taken in the foreseeable future – and that he should therefore escape Kabul now, while he still could. So a friend of his sold a field he owned, loaned him the money to pay the smugglers and in the height of bitter winter in December 2014, Khushal began his journey west.

Knowing how arduous such an odyssey was likely to be, I tried to get funds to make a documentary showing the journey from Khushal’s perspective, confident that audiences would share my outrage and horror. While the film was never commissioned, I spoke regularly to my old comrade throughout his journey. The imprisonments, beatings, robbings, shootings, near-shipwrecks and other privations he endured came sharp on the heels of two years standing shoulder to shoulder with our troops in Helmand. So when he finally arrived in Calais and found the door tightly shut, I felt obliged to try and shame the government into helping him. I decided to attempt to make the final leg of his journey by his side.

We didn’t get far – although we weren’t actually “caught” as has been reported. On the ground, my presence was definitely more of a hindrance than a help. I am also aware that a night in the Calais “jungle” and some scrabbling about the fences of the Channel tunnel terminal with an old friend trying to break back into your own country is no real hardship and, quite frankly, probably a little silly. Nonetheless my presence there was a morale boost for a much abandoned man and I hoped the gesture would win me a small platform from which to campaign for him.

The government has refused to help a translator who worked for Cameron himself in Afghanistan

With the recent news that another Afghan interpreter who worked for the British has been murdered by the Taliban, and the refusal to help a translator who worked for Cameron himself in Afghanistan, the government’s position on the issue seems increasingly incomprehensible. But if they are too hard-hearted to see the charitable imperative to help people like Khushal, perhaps I can offer them two motives of self-interest.

Firstly there is any amount of (frankly rather justifiable) cynicism abroad about the motivations and moral integrity of UK foreign policy. Spectacularly feeding to the wolves the vulnerable men and women who have stood by us is no way to abate this. Secondly, the debate at home over immigration has become embittered precisely because policy has for so long been serenely disdainful of mainstream public opinion. Conversely, looking after those like Khushal is a move that would win the government approval across the board. Please join over 10,000 people in signing my petition on change.org to help me make this point.