Among David Lammy’s numerous critics, none may find more satisfaction in his turbulent week than a particular French taxi driver.

“Oh dear, it’s one scandal after another with your Deputy Prime Minister,” remarks Nassim Mimun, feigning disapproval as he peruses his copy of La Provence. Lammy’s recent missteps have clearly captured attention not just in Britain, but also in the south of France.

“Your minister is a disgrace… Lammy brings great shame upon your country, but I’m pleased he’s facing trouble because he’s a dishonorable, wicked man,” Mimun adds.

After blundering in the House of Commons regarding prisoner release errors, Lammy is now under significant pressure, facing unrelenting scrutiny. His conduct was described as “cowardly” by none other than a Cabinet colleague.

Yet, Mimun’s criticism strikes a particularly personal chord. The taxi driver and minister share a past, with Mimun alleging that Lammy turned his life upside down.

The animosity traces back to the early hours of April 11 at a mountain resort in the French Alps. It was here that a heated dispute over a taxi fare erupted between the two men following a seven-hour journey from Italy.

That much is undisputed. Untangling the criss-crossing claims surrounding the 360-mile trip and its aftermath, some involving Mr Lammy’s wife, Nicola Green, is another matter.

During the altercation over the fare, Mr Mimun says the then Foreign Secretary, sitting behind him, punched or kicked the back of his seat, shouted about the ‘f***ing French’ and slapped his neck. ‘He was going crazy,’ says Mr Mimun.

Taxi driver Nassim Mimun claims Deputy Prime Minister David Lammy has ruined his life. In April the pair argued over the fare of a seven-hour journey from Italy

Lammy and his wife Nicola Green in April this year. Ms Green told police that at one point Mr Mimun showed her a knife in the glove compartment

‘I thought he was going to come for me and that there would be a fight. That’s why I drove off.’

Ms Green told police that at one point Mr Mimun showed her a knife in the glove compartment – while he says he saw a holster on Mr Lammy’s hip and assumed he was carrying a gun.

He says he was so convinced that the Foreign Secretary was ‘packing’ that, as he sped off after the row, Mr Mimun slid down his seat lest Mr Lammy tried taking pot shots at him.

Of course, there was no gun. Just as police found no knife. What Ms Green saw, says the chauffeur, was a silver pen. Nothing is quite what it seems with this affair, and much is still unexplained.

Why for instance would Ms Green, as Mr Mimun claims, open her door while he was doing 75mph on a motorway? What led to this dramatic act?

Mr Mimun offers only that she seemed in a filthy mood and wanted to get out of the car even though a service station – ‘as I repeatedly told her’ – was only a couple of minutes away.

Things didn’t augur well for the 360-mile trip, he says, when, before they set off, she turned her nose up at his Ford Kuga – described as a compact SUV – after requesting a Mercedes with leather seats.

‘She was cold with me and grimaced when she saw it,’ he says, while her husband ‘asked about its horsepower’. This was when things were still relatively cordial.

Nearly all of what would later unfold as the atmosphere in the car soured remains contested but one crucial issue has now been put before a judge. The Lammys allegation – that Mr Mimun stole their luggage and 700 euros (£616) – was rejected by a court in Bonneville, eastern France last week.

Claiming a memorable victory ‘for the little guy’, Mr Mimun tells The Mail on Sunday that where once the odds were stacked against him, ‘at last the tide is turning’.

He says it was ‘cruel’ for Mr Lammy and his wife, both 53, to accuse him of stealing ‘as the sum he says I took in cash was the exact equivalent of what I was owed’.

The Lammys travelled some 360 miles from Italy to the French ski resort of Flaine

He adds: ‘This made the police think I was guilty… Thankfully the court believed me. This was nasty – I could have gone to jail. It is Lammy who is the thief, he hasn’t paid me the extra sum I was owed.’

The Lammys vehemently dispute all the driver’s allegations. Whatever the truth, though, this was an unseemly affair that, as one French diplomat observed wryly, left the entente cordiale, if not broken, then fleetingly bruised.

Before meeting Mr Mimun on April 10 at Forli airport in Italy, the couple spent four days accompanying King Charles on a State Visit involving tours of the Colosseum and the Quirinale Palace in Rome.

When the royal party departed, the Lammys stayed on for a holiday and headed for a hotel in Flaine, a ski resort in Haute-Savoie. They resolved that despite being near an airport, the quickest route, counterintuitively, was by road.

A Foreign Office official booked a car through GetTransfer, a Cyprus-based booking platform and the agreed fare, of around £717, was paid directly to the firm by the UK Government. It is understood that the Lammys had agreed to refund the cost later – a standard arrangement for a minister using officials to arrange what is effectively a private journey.

Mr Mimun learned of the job two days day before when, he says, there was no mention of their status. He was only told he was driving the UK Foreign Secretary shortly before they were introduced.

‘I was annoyed as it becomes a different story when there is a senior government figure involved as there are security implications,’ he says. ‘This is always the way. I have driven all sorts of French ministers, ambassadors and VIPs.

‘I said [to a member of Mr Lammy’s entourage] that I wouldn’t do it for that price.

‘If I’d known he was such an important figure, I would have charged a lot more. This is standard.’ He claims the entourage member consulted the Lammys and it was agreed they would pay an extra 700 euros ‘at the other end’. Again, the Lammys dispute this version of events, and it is inconsistent with an account the driver has previously given.

The son of a chauffeur firm owner, now dead, Mr Mimun lives in the city of Avignon in south-eastern France’s Provence region, where he was born. He shares a well-kept house with his mother, sister and nephew and has been a chauffeur himself for 20 years.

Over dinner he shows the MoS an exchange of text messages with the Foreign Office’s ‘head of events and trips’. In a message from 5.34pm on April 10, Mr Mimun sends her a picture of his location and says that ‘you have to leave the airport, I’m not allowed to go in… I’m two metres away [from the entrance] next to the police’.

The official says: ‘Great! My colleague will find you.’

To his surprise, he wasn’t subjected to any security checks and nobody so much as gave his car a once over.

When on the road, he briefly made small talk with Mr Lammy. Then he says the politician discussed the Israel-Gaza war with his wife before both fell silent for 30 or 40 minutes. He thinks Ms Green dozed off.

Mr Mimun says an hour or so later, Ms Green began complaining. ‘She wanted to sit in the front, and I said we could stop at the next service station, but she suddenly lost it and opened her door. I undid my window and put my arm around to close it. It was terrifying.’

The Lammys allegation – that Mr Mimun stole their luggage and 700 euros (£616) – was rejected by a court in Bonneville, eastern France last week

Mr Mimun says the then Foreign Secretary, sitting behind him, punched or kicked the back of his seat, shouted about the ‘f***ing French’ and slapped his neck

Then he slowed down and pulled over on the hard shoulder. ‘I put on my hazard lights and she moved into the front. We were 900 metres from the rest area.’ He says she muttered something about the ‘f***ing driver’. He adds that Mr Lammy ‘sat there and said nothing’.

Neither did he seem fazed by what Mr Mimun claims happened next. He says Ms Green was ‘throwing rubbish out the windows, including the bits of a sandwich she didn’t eat, biscuit wrappers and drink cans’.

‘I started getting other cars flashing at me,’ he says. ‘The Italian drivers weren’t happy about this.’

What could have prompted this bizarre – albeit alleged – behaviour? ‘I don’t know if there was something going on between her and her husband,’ says Mr Mimun. ‘Maybe something happened before I picked them up.’

Some hours later, after calm was restored, Ms Green seemed to begrudge him stopping for a brief rest and to fill up with petrol.

Mr Mimun says he heard her complaining on her mobile to the Foreign Office official who he assumes must have contacted GetTransfer because he then received a message from the company asking why he had pulled over. He told them it was his statutory right.

It was after 1am when they reached their destination in the Alps. Mr Mimun says of the exchange that ensued: ‘Lammy wasn’t happy about having to pay extra. He asked to pay by credit card and seemed surprised when I produced a payment terminal.

‘Still, he didn’t take out his card. He wanted a receipt but I wouldn’t give him one until he paid me. I started writing out a bill and he tried to snatch it from me.

‘Then he starts saying, “f***ing French, f***ing French” and I took several blows.’ Demonstrating, he says: ‘He hit me here [on the neck] with the palm of his hand. Then he gets out of the car, angry, and I saw him walking round the car, and I was afraid.

‘He was coming towards me and I thought maybe he was armed, that maybe he had a gun in the holster I saw in Italy. I thought he wanted to fight and I didn’t want to fight.

‘After a few minutes I said, “Siri, call the police!”’

The voice-activated digital assistant put him through to officers in nearby Switzerland who promised to register his complaint but advised him to report the incident to French police.

Mr Mimun alleges he decided to report his passengers to police in the French town of Cluses, the nearest open Gendarmerie, 12 miles away. After making a statement he was back on the road.

It was several hours later, he says, that it dawned on him that he still had the couple’s luggage in the boot. Quite possibly, he concedes, his memory was jolted by a text message from the Foreign Office official at 9.32am: ‘Can you please confirm when you will return the bags to Flaine. We need them urgently. This is now a crime and I had to alert the authorities.’

Mr Mimun turned back, though is insistent that driving off with the luggage was an honest mistake. In court, it was alleged that after they got it back the Lammys found 700 euros were missing. But Mr Mimun’s lawyer, Guillaume de Palma, said the couple’s claims were ‘incoherent’, adding that ‘there is nothing to show that the bags were opened [by Mimun]’.

Reflecting on what he calls the worst drive of his life, Mr Mimun argues that it raises ‘questions about Lammy’s character’. Not that he has captured the moral high ground. His own complaints about Mr Lammy’s supposedly aggressive behaviour, after all, were rejected by prosecutors.

A government source said: ‘The driver’s claims about the David Lammy and his wife are total nonsense, just like his claims that they didn’t pay – which GetTransfer has confirmed was paid in full.’

But whichever side is to be believed, it is an article of faith that our Foreign Secretary – our principal diplomat – comports himself with dignity at all times. To lose one’s rag on the international stage, at a vital summit for example, might have potentially far-reaching geopolitical consequences.

And while a football fan shouting about the French after England are outshone by Les Bleus is one thing, to hear them from the lips of the holder of such distinguished office would be quite another.

‘This has turned my professional life upside down,’ says Mr Mimun. ‘Because of your minister… I wasn’t able to work for seven months [as he was placed under judicial supervision].’

He takes us to the garage where his now-dusty Ford Kuga languishes with a flat tyre. ‘It has been repaired but I cannot pay the bill. But when I get the money together I can work again as the court case went in my favour.’

For once, he smiles.

And at least he’ll have a story to tell his clients.

‘I had that Foreign Secretary in the back of my cab the other day…’