I faced life in jail ... just for writing about Milton Keynes

Happy memory: Sally and autistic son James at a local charity ball in 2006. When her arrest made it impossible for her to look after him, she had to have James placed in a care home

Ironically, it was with a feeling of smug satisfaction, so pitifully rare in my life as a disorganised journalist and busy mum, that I stepped out on that sunny May morning to buy wallpaper for my youngest daughter Kate's bedroom.

My children were happy: they were reasonably polite and I usually managed to feed them vegetables.

Our cottage, into which we'd moved just six days previously, was finally resembling less of a builders' yard and more of a dwelling place.

And my career ran pleasantly and reliably on the well-oiled wheels of an entire working life spent in the same busy town.

I was born in Milton Keynes when it was a village. I completed my journalistic apprenticeship on one local newspaper and I was still there, 32 years later, on another.

I'd worked part-time for 20 years to fit in with the needs of my autistic son James, but I knew the town inside out.

My dog-eared contacts book bulged with trusted names and numbers. There were councillors, local dignitaries, gossipy hairdressers, teachers ... and, of course, police officers.

That sun-soaked morning last year, there was no flicker of premonition that my world was about to be torn apart in a frenzy of police officers, criminal investigations and court proceedings that would threaten not just my own family life but the country's perception of Press freedom.

I hadn't a clue, as I shopped in Laura Ashley, that eight plainclothes police officers were poised to arrest me, lock me in a cell, interrogate me, strip-search me and finally put me in the dock for a multi-million-pound Crown Court trial after which I could technically be sent to prison for life.

I had no understanding of what heinous crime they thought I'd committed.

Officially, I was charged with three counts of the ancient common-law offence of aiding and abetting misconduct in a public office - the same charges levelled at Shadow Immigration Minister Damian Green last week when he was arrested over claims he had leaked confidential Government documents.

I recall how, in that heart-stopping moment when the police arrested me, I misunderstood them and, clutching my Toile de Jouy wallpaper to my chest, declared I was far too old to do indecent things in public places.

I'd never done anything naughty outside, I assured them. 'Well, not since I was about 17,' I remember adding stupidly.

They must have thought I was crazy, babbling on about al fresco sex. In fact, I was being accused of encouraging a police officer to give me information - stories the police authorities do not want in the public domain.

Each of the charges referred to stories I had written or cases I knew about.

None of the stories could be described as being of national importance. One concerned a local footballer involved in a brawl, another about the death of a former drug offender and a third, which was never published, involved an Islamist released early from prison.

But these officers weren't like the old-style coppers I knew, ones who enjoyed a pint with a journalist, exchanging moans about the spate of local burglaries, a sigh over the criminal justice system or perhaps a tip-off about an interesting court case that was coming up.

Those officers were my friends. Local newspapers cared about their community, and police officers devoted themselves to keeping that community safe. We were their conduit to the public. We helped each other.

It all changed with one phone call. My mobile rang as I drove home from Laura Ashley.

Before the storm: Sally and her daughters at a friend's wedding just before she was arrested. Kate's face has been obscured at the family's request

Perhaps it was a problem with James. My partner, Kate's father, was working away, so domestic duties that day were my responsibility. Worried, I risked answering the call while driving.

'This is Inspector Gary Young.' 'Oh hi, Gary.' Did I know him? Did he want me to write a story? The answer to both questions was no.

'I want you to drive home immediately,' he said.

My hands slid on the wheel as I tried to steer into a lay-by. Something was wrong.

'Tell me,' I pleaded. 'Are they OK?'

'Your children are fine.' He sounded almost embarrassed. I heard the word 'arrest'.

He was arresting me - by telephone, while I was driving.

I drove the seven miles to our Bedfordshire cottage. By now my phone was beeping with messages from my office: 'Police are everywhere. They've seized your computer. They're taking your notebooks ...'

As I pulled into my driveway, I was surrounded by police. It was so surreal I could barely register the fact that they were searching my car, my house, even my garden shed, asking about documents, bank accounts, notebooks. Dumbly, I did the only thing I could think of: I offered them coffee.

'Gosh,' I remember saying, 'you're my very first visitors in this house. Do you take sugar?'

When one WPC upended a box of builders' receipts, I was puzzled. When another rifled through my purse, I was mystified.

But when officers trooped towards my children's bedrooms, the true horror struck. 'What are you looking for?' I demanded.

Slowly, I realised this Sweeney-style nightmare was connected with Mark Kearney, a police officer about to retire after 30 years' service.

Mark and I had met in 1992 when he was the Milton Keynes police Press officer and I was a single mum.

It was common knowledge that we'd been in a relationship and, when it ended, we were still best friends, speaking daily on the phone.

To my son, Mark had always been a mentor and a hero: he had been an invaluable help in the daily battles generated by autism and learning disability in a lively young man who needed round-the-clock supervision. Now Mark had been arrested, too.

In my befuddled state I spotted two officers wearing white space-type suits in my garden, more of them under my car. Was I hallucinating?

Panic set in when they bagged up my mobile phone and address book containing numbers for childminders and James's helpers.

Sally was amazed by the parallels between her experiences and those of MP Damian Green, pictured leaving his West London home this week after nine hours in police custody

With a landline still to be fitted in the cottage, these people could no longer call me.

Domestic worries swirled around my head.

I needed to get our computer fixed so my eldest, Lucy, could download her GCSE coursework. I had to collect ten-year-old Kate from school. I had to check on James, out with a relative. And I'd promised Kate we'd collect her long-awaited new kitten.

'I'm so sorry, but I really must go,' I told one officer. He blinked twice and said: 'You have to come to the police station with us.'

I was ushered into a car and allowed one phone call - to Kate's father. 'Help,' I sobbed. 'The police are taking me.'

Although the local police station was two minutes away, I was taken 40 miles to Banbury because these officers were from Thames Valley Police Professional Standards Department. Ah . . . The people who 'police' the police.

But why me? I agonised, as they fingerprinted, photographed and stripped me of every belonging apart from one tear-stained tissue.

The cell door closed. I sat on the bunk, staring at the concrete walls, the lavatory bowl and the cameras that watched me. I was desperate for the loo but terrified they would see me. And there was no loo paper.

My watch had been confiscated but I knew it was night-time. I remember, in a blur of darkness, begging for the medication I take four times a day to prevent migraine attacks.

I was crippled with worry about my children - and I would have sold my soul for a roll of loo paper and a bar of soap.

The interview, when it finally took place the following afternoon, was a blur of bizarre allegations about paying police officers bribes and selling stories to national newspapers for huge sums.

'Don't say a word,' warned my legal adviser. I ignored him. I had nothing to hide.

'Yes, journalists sell on the odd story,' I said. 'No, local papers never pay for stories. Yes, of course I have local police contacts.'

Name them, they said. I shook my head. Under the Press Complaints Commission code of conduct all journalists have a 'moral obligation' to protect their contacts.

We paused for a Superintendent's Review: I'd been detained for so long they now needed higher authority to question me further.

That was when, to employ a cliché I've probably misused hundreds of times at work, the bombshell dropped.

This man I'd never met before looked me in the eye and said: 'You are under investigation for an extremely serious offence. You could go to prison. For life.'

Vindicated: Sally after the charges against her were dropped this week

The words were still ringing in my ears when I was discharged that evening into the arms of my bewildered family.

'Don't worry about my coursework, Mum,' whispered Lucy.

'I can wait a bit longer for my kitten,' said Kate, bottom lip trembling.

'Hey Ma, where've you been?' grinned James, blissfully unaware.

The months that followed were grim. The second interview was preceded by a strip search (naively, remembering the previous battle for my migraine medication, I'd popped a couple of pills into a pocket).

I was played tapes of Mark and I talking on the phone and in the car. We'd been bugged for weeks, if not months - this all took place after our relationship had ended. I listened to our gossip, our harmless chitchat.

One officer told me, disturbingly, that it was still an offence merely to listen to details from a third party.

It was only afterwards that it dawned on me what sinister implication this case could have for journalists all over Britain. Indeed, it would be highly unusual for a journalist not to have off-the-record contacts.

Technically, thousands of my media colleagues could be arrested just like me.

I had no idea then that 'the Murrer Case' would spark such outrage about Press freedom and that I, a middle-aged mum of three working 12 hours a week on a local paper, would be at the centre of this controversy.

At the time I simply felt violated. How dare these people bug my conversations and even download texts from my daughters?

Mentally I was numb; too tired to care about anything except my children. If I was going to prison then I'd better, for the first time in my life, get organised.

I rushed around a year early to choose a secondary school for Kate. Clever Lucy, who'd achieved straight As at her GCSEs, was steered into sitting for a scholarship for the most caring boarding school I could find. I couldn't nurture her through A-levels and university, but Stowe staff could - and indeed are.

Finally, I made the hardest decision of all: I asked Social Services to place my lovely but needy boy into a residential care home. Today he's flourishing and comes home regularly. But it still hurts.

Sometimes, during those dark days last autumn, I found myself wishing for a terminal illness: anything, I thought, must be better than this hell.

The cure for such self-indulgence was my work at the Milton Keynes Citizen. One day I interviewed a lung-cancer sufferer who was going to run a marathon. Another day I wrote about parents who had lost a child. I knew I had to get a grip - and fight.

Ironically, it was better after I was charged last November. I knew it was coming - bizarrely, I had a tipoff from a police contact - and the brilliant team of defence lawyers who had come to my aid could finally snap into action.

Earlier this month, the legal arguments began in Kingston upon Thames Crown Court to determine whether there was enough evidence for the case to go to a full trial.

Mark and I weren't the only ones in the dock: Mark's son Harry and private detective Derek Webb were also charged with aiding and abetting misconduct in a public office.

In preparation for the trial, I'd packed seven weeks' worth of clothes, rented a room in Kingston and organised an au pair for Kate. She was too young to understand what might happen - all she knew was that Mummy was going to London on a job 'to fight for journalists'.

I've reported from court many times, but sitting in the dock behind bullet-proof glass designed to detain terrorists was bewildering. I held a Woolworths notebook in hand and tried taking notes on my own trial.

What I discovered was shattering. I came to realise that the case wasn't about me at all, but the rights of every journalist in the country.

My defence barrister, Gavin Millar QC, told the court that, under Article 10 of the Human Rights Convention, my right to freedom of expression had been breached by the State. Thames Valley Police had no right to have bugged my conversations with Mark, a confidential source, and my arrest was also unlawful.

Furthermore, the stories I had written were accurate and the information was already in the public domain.

Millar went on to argue that journalistic privilege, unless it posed a genuine threat to national security, must extend to a reporter's sources, otherwise no confidential source would ever again speak to a reporter.

His argument, which ran for eight-and-a-half hours, was described by Judge Richard Southwell as a masterclass on journalistic human rights and the freedom of the Press.

The charges against me, Mark, Harry and Derek were knocked down as Judge Southwell ruled the evidence inadmissible in court.

The case has now been thrown out and, after 18 months, our ordeal is over.

When I heard about the arrest of Conservative MP Damian Green last week, I was amazed at the parallels between his experience and my own. I felt sorry for him. In fact, it's the first time in my life I've felt a natural affinity for a Tory MP.

My own victory in court has been hailed as a landmark triumph for Press freedom, and I expected to feel vindicated and victorious. But I still feel numb - and angry.

First there's the financial cost. Had it gone to trial, the case would have cost more than £4million, but it still ended up using more than £1million of public money.

And then, of course, there's the emotional toll. After something like this, I wonder how it's possible to return to a normal life.

I tried to keep working, but I don't know if I have the strength to continue as a journalist. I certainly won't be doing another police story again.

Most importantly, though, my children are happy and healthy. And, after 18 months of shifting perceptions and crazily changed values, that is truly all that matters now.

• Sally Murrer has requested that her fee for this article be donated to the National Autistic Society.