It’s a strange day when you head off for a quiet walk in the country to track the footsteps of Vincent van Gogh and come within a whisker of being frog-marched off to a holding cell behind barbed wire, not to mention a good beating.

It all happened last Sunday. A family walk with friends up the river at Auvers-sur-Oise, a few miles to the north of Paris.

A hint of rain, a sliver of sun, a picnic in the backpack, a stately line of cypress trees, the dogs and kids running ahead to check out the swans and the ducks, the paunchy journalist bringing up the rear. A merry band indeed.

The purpose: to find out more about the town and area where Vincent van Gogh spent the last three months of his life. It was in Auvers on July 27, 1890 that he put a revolver to his chest and fired the fatal bullet.

He was a better painter than marksman to be sure. No swift suicide (if it was indeed suicide for in 2011 came a suggestion that Vincent had not in fact shot himself, but that two boys with a misfiring gun had pulled the trigger); instead the bullet ricocheted off a rib and lodged in his spine. It took two days for him to shuffle off his mortal coil.

His brother Theo died of illnesses caused by syphilis six months later and is buried alongside Vincent in Auvers.

The cemetery was just one of our stops. Another was the house where Vincent expired and the church that he immortalised in paint. The town of Auvers has traded well on a painter who spent just three months there – a museum of absinthe has also claimed its place among the drifting lanes.

The day, though, belonged to another less than merry band of spycatchers who appeared from nowhere to pounce on me along the riverbank.

One of our fellow walkers, who lives in Auvers, had explained that along our path was the house where the last Shah of Iran lived in exile after his fall from power in 1979. I was under the impression he had spent his time buzzing around the USA getting treatment for his cancer, Morocco, Mexico and Egypt where he is buried.

Be that as it may, I am a sucker for what you might call “living” history. Iran remains very much in the forefront of the world’s news and so I was able to use the Shah as a pretext to explain to the kids what had happened there in the 1970s. And what is happening now. They laugh at the thought of a president called Ahmadinnerjacket but rush back to join the dogs and the ducks.

Until we reach the residence with its long, high walls topped with barbed wire, lights and, unseen by me at the time, security cameras. Just over the wall, we could pick out the sloping roof and top floor of a grand residence.

“It’s like a prison,” they said.

“Well, I suppose it was,” I replied. “A man in exile, fearful for his life, barricades himself into his palace. In spite of all his money, he doesn’t have any freedom. He can’t just walk along the riverbank like us.”

The kids nod, a moment in thought. And then screech and chase each other with the sticks they have picked up along the way. The dogs start barking and games of Tag and Fetch begin simultaneously up ahead.

A house that is interesting for its history, I thought. Maybe I can put in a line about it if/when I blog about this lovely day out following van Gogh (or Gog, as the French prefer to say). And so, as my colleagues walked ahead, I fetched out the camera and lined up a shot of wall, wire and rooftop. Just one. Nothing special. Then returned the camera to its case.

Before I had stepped three paces, a sidedoor had opened and a man slithered out, walkie-talkie in hand and approached me.

“Bonjour,” he greeted me.

“Bonjour.”

“You just took a photograph.”

“Yes, fascinating place. I understand the Shah lived here.”

“No, not the Shah. But you are not permitted to take pictures.”

Generally, I am quite amenable to people’s requests but I took umbrage at the man’s aggressive tone.

“Who says?” I asked.

“We don’t allow it.”

“Who is we? Are you with the gendarmes?”

“No, I am not police but you are not allowed to take photos.”

“But who says? Do you have some kind of ID? Are you with French state security? Who are you?”

I thought it best during this exchange and throughout all that followed not to mention that I was a journalist.

He didn’t answer me, just began talking into his walkie-talkie. Not in French but, I guessed, in Persian. Within moments another three men appeared from the magic door and the four of them formed a circle around me.

A different one spoke, slightly younger than the others, a scar just under his left ear.

“Where are you from?” he asked.

“Where are you from?” I returned.

“Why are you taking photos here?”

“Why don’t you want me to take photos here?”

A pause before the scar tried again.

“You are English aren’t you?” he asked in English, adopting a softer tone.

“As it is yes, I am. And you are Iranian, are you?”

“I know England very well. I was a student in Newcastle. I lived in Bristol and Manchester. I know it very well.”

“Good stuff. Wish I could say the same about Iran but I haven’t ever been. ”

“Please, we don’t like people taking pictures. For security reasons.”

“So who lives here then? The son of the Shah?”

“No, not the Shah. No. We are the official opposition, the NCRI (National Council of Resistance of Iran). We are fighting against the government of Iran. They have people who are trying to do us damage and we have to be careful about our security. That is why we cannot allow you to take pictures.”

There are moments when the fight is worth fighting and there are moments when it really doesn’t seem terribly important. I suspect the Iranian secret service know perfectly well where the opposition is so I didn’t believe the security aspect of their argument but even so this one just didn’t seem important. It was a pretty lousy picture anyway. Besides I was reading John Le Carré at the time and had visions of my ending up gagged and blindfolded in a cardboard box while my co-walkers continued along the riverbank blissfully unaware of the drama unfolding behind them.

“I see. Well, I certainly don’t want to put anyone in jeopardy (not least my family, I thought). So I will gladly delete it. The only problem is that this is a new camera and I don’t actually know how it works. I will have to get my daughter to do it.”

Feeble as it sounds, this was absolutely true. As a technophobe, I need a good couple of hours with the instruction manual before I can do anything. My children need five minutes and no manual.

“No, I am sorry. We cannot allow that. We have to delete it now.”

“Well, as I said, I don’t know how to. It is a new camera and I am not going to let you take it away. I give you my word that it will be deleted and that it will not be shared anywhere.”

“No. We have a man who understands these things.”

More talking on the walkie-talkies and a fifth man appears through the magic door, this one twice the size of the others put together. Immense but smiling which is always a touch sinister. I definitely wasn’t going to argue although I did warn him that he had better be careful.

“There are a lot of family pictures on there and some films. You delete those and you will have to answer to my wife. She’s Welsh and a lot scarier and tougher than me.”

The giant didn’t look unduly concerned about the prospect of a Gallic onslaught as he delicately worked the buttons on the camera which was like a toy in his bucket hands.

“This one,” he said.

“That is it. Like I said, just the one picture.”

The giant pressed the Erase button and then Confirmed.

Smiles all around; suddenly their anxiety was lifted and we were all chums, apparently united in the war against the regime in Iran. I kept my mouth shut.

“So,” said the scar as I made to move off. “This is our embassy. You can come in if you like. Would you like a coffee? Good Iranian coffee.”

I will admit to feeling confused by this swift transition from public enemy number one, the master spy angling to bring down the opposition in exile, to brother in arms. Had I been a spy, I imagine I would have seen a lot more from inside the compound. But maybe they still suspected me and were trying to lure me into that cardboard box which could then be dumped from 30,000 feet over the Persian Gulf.

I declined politely, explaining that while an Iranian coffee would be absolutely perfect, I had to catch up with my family and my friends. I wished them good luck in their political endeavours and marched off along the riverbank.

Van Gogh was waiting.

Barney Spender 2013