‘Put down your tools or we’re taking you in,’ demanded Police Constable Ives. He was talking to me. It was late one April evening and we were both standing on the verge of the dual-carriage roundabout in London’s wretched Elephant & Castle. I was holding a finely crafted oak-handled stainless steel border fork and he was dangling handcuffs.

For four years I have been a guerrilla gardener, by which I mean an illicit cultivator of neglected patches of public land. I ‘fight the filth with forks and flowers’ and until now had never been confronted with the choice between arrest and retreat from a dig. There have been skirmishes with the law – a brief questioning about our weeding, a couple of false terror alerts about the contents of my car (it was heavily laden with sacks of wood chippings not bomb-making equipment) – but all encounters had been civil and sometimes even quite encouraging. This time it was heavy.

PC Ives and I were not alone with the swirling traffic. Alongside me were six other regular guerrilla gardeners and two film crews, including one from a Swedish children’s TV show. For half an hour we had been weeding and clearing litter in a corner of the shabby roundabout and talking to the cameras. The disruption began when Ives’ Vauxhall Astra careered clumsily along the roundabout’s central footpath and stopped behind us. Another car drew up and soon the police outnumbered our ragbag international force of lawless gardeners and media. Eight or so officers (I was in no state to count) stood around us tensed as if waiting for a penalty kick and grim reinforcement glared from a fluorescent police minibus.

An hour earlier the director from the Swedish show had been coaxing us into ‘looking dodgy’ and said something about wanting to ‘spice-up’ what was otherwise an educational broadcast for English language tuition. He seemed anxious that his film of well-spoken gardeners tidying up a corner of central London might be dull to Swedish children so had contrived moody shots of us marching in single file down my tower block’s dark public corridors with spades and forks over our shoulder. We had refused his urge to film us trying to hide behind lampposts, now he refused the police’s request to put down his camera. The other cameraman articulated his media rights, ‘I am allowed to carry on filming.’ ‘But don’t show my face,’ said Ives. The Carry On continued and with police lights and cameras on our action I took centre stage. The conversation continued something like this:

‘Please explain what it is you object to?’ I asked.

‘You are causing criminal damage.’

‘What is criminal about clearing weeds and litter?’

‘You do not have permission.’

‘No one objected to my display of nasturtium on this roundabout last summer nor the forget-me-nots just over there.’

(I don’t remember their reply to this, but I do remember them getting more agitated. One of the policewomen muttered into her radio something about. So I continued.

‘Why don’t you go and catch some real criminals rather than waste your time stopping local people tidying up this shabby area?’

‘You could be doing anything.’

‘Now you know we’re gardening please leave us alone!’

‘You’re vandals.’

‘Yes, vandals with flowers.’

I was getting nowhere. The police were robotic and increasingly jumpy. The others were silent and potentially more nervous than me in my adrenalinepumped performance. So I changed emphasis and gave them Establishmentfriendly facts.

‘I actually have permission from Southwark Council to garden on the other side of the street. They gave it after I had guerrilla-gardened there for three years. And you know what? They told me they would never have granted it if I had asked them first.’ Surely, I thought, this would melt their resolve; here was evidence (well, a claim at least) that I could work with the council but that a precedent was set that to do so legitimately I must first demonstrate horticultural vision and commitment? But it was futile. To these police it was as if ‘the other side of the street’ was the jurisdiction of another country. Which made my desperate and boastful grab to persuade them with an American vice-presidential celebrity endorsement failed too:

‘Al Gore loves what we’re doing.’ (The god-like eco soothsayer had said, ‘they’re grrrreat’ to British chat show host Richard Madeley.) But this plea was ignored by Ives and his squad without so much as even a raised eyebrow.

And so I had to choose: arrest or retreat? It was an easy choice. I retreated.

There was no need to be taken in to custody. I needed no additional headline grabbing drama because the whole ridiculous encounter was already being reported. And if we were to complete our garden it would get done sooner if I were not behind bars. So we carried our tools home and the media followed. I was angry and depressed – how could the police be so stupid? But I was also excited – we do not use the word guerrilla lightly to describe our gardening, and here, on film, was evidence why. As we rode the lift to the top floor of Perronet House we began discussing what to do next. Should we just leave the bare new patch for a while and let the situation cool? Or could we slip back and finish it off? After a bottle of wine the choice was easy. We went for victory.

From the safe haven of Perronet House we darted across the road two at a time in short sharp bursts and plunged our depotted purple primula, lavender and campanula into our curved bed beneath the chevron sign. As is often the case, when we dug deep we found remarkably healthy soil, imported purposely for planting. Such riches are a reminder of the ample budgets and naive idealism of landscape architects when they construct grand new traffic intersections. Sometimes, beneath the mat of weeds and litter, we also find plastic plant labels and old root systems, archaeological relics of a briefly glorious landscape. Encouraged by the vitality of the land we pushed on. Never have we gardened so fast and nor with such excitement. But never has a new guerrilla garden seemed so vulnerable.

For a while the incident nagged me, anxious that more time-wasting police threats would be repeated but three months on the garden is thriving. Last week I was out there on my own brandishing a watering can when a police car drove past. Seeing it made me flinch but the two officers inside turned to me waved, and cheerfully beeped their horn. The flowers must have won them round.