The figure walking across the dark car park was one Sally Challen recognised immediately. Of course she did.

After 30 years of marriage she would have known that gait, that profile, anywhere. It was her husband Richard, locking his car and jauntily trotting across the road — straight through the doors of a well-known local brothel.

Sally's heart was pounding as conflicting emotions ripped through her. Fury, that he was betraying her, his loyal wife. Disgust that he was paying prostitutes — women who were likely damaged and exploited — for sex. And triumph, that she'd 'got' him at last.

Controlling: Sally with Richard at a dinner in 2004

He couldn't wriggle his way out of this one. Finally, he'd have to own up to his appalling behaviour.

An hour passed, and there he was again, returning to his car. 'He saw me and legged it,' she says.

A farcical scene ensued as they raced their cars through the Christmas-lit streets of suburban Surbiton, with Sally screeching to a halt outside the family home three miles away in Claygate, Surrey. But Richard had got there first.

'I ran into the kitchen and found him calmly making a cup of tea,' says Sally. 'I shouted that I'd just seen him coming out of a brothel and he looked me straight in the eye and said, 'what are you talking about, Sally? I've just been out selling someone a car. Honestly, I don't know where you get these ideas. You're bloody going mad.'

She'd caught him red-handed, but his indignant, flat denials were so convincing it left her thinking that perhaps she was going mad. In the face of such certainty and insouciance, who wouldn't have been left doubting themselves?

If one incident sums up the devastating mind games that Sally Challen was subjected to during her marriage to Richard, it is surely this one.

The couple on holiday in France with sons David and James in the 1990s

But the 'brothel incident', as Sally calls it, was just one in a huge, painful dossier of horrifically cruel and controlling behaviour she endured throughout her entire adult life at the hands of the man she still, to this day, describes as 'the love of my life'.

Outwardly, this middle-class mother-of-two had an enviable life. A successful car salesman for a husband, she lived in a double-fronted, four-bedroom, £1million house and their two sons went to expensive, private schools.

She had a good job as an office manager for the Police Federation. Yet what nobody knew was that for more than three decades she was also psychologically tortured, and subjected to vile sexual abuse at the hands of her own husband.

The torment Sally suffered left no bruises. No one had a clue what was truly going on until the day, in August 2010, when she finally snapped and killed Richard in a brutal hammer attack.

Driven to breaking point, she inflicted at least 18 blows as he sat eating a meal, before covering his body with blankets, changing out of her blood-spattered clothes and driving away with a plan to commit suicide.

Painted as a vengeful, jealous wife in court, Sally spent nine years in prison for murder.

But a change in the law in 2015, when coercive control finally became an offence, enabled Sally to appeal her conviction, which ultimately led to her charge being reduced to manslaughter.

Her legal team were able to argue that she was incapable of making a cold-blooded, premeditated decision to kill Richard, as all rational reasoning had been destroyed by the years of abuse she'd suffered.

Having been released from prison earlier this year, her case is now cited as one of the most shocking examples of coercive control the UK has seen. It has set people thinking about what goes on behind closed doors.

Wedding day: Sally and Richard in 1979

Starting today, in a series of shattering exclusive interviews —Sally's first — she describes the moment she ended the life of the man she never stopped loving.

She recalls how she was pressured into an abortion by him as a teenager, and the numerous times he raped her during their long marriage, as well as his constant lies and many affairs.

She tells how her sons, who only became aware of the full extent of her suffering after their father's death, have stood by her, of surviving nine years in prison and how she is now rebuilding her life as a campaigner for other abused women.

Now 63, Sally could be anyone's mum. Acquaintances at the time of her 2011 trial described the woman they knew as someone who wouldn't hurt a fly.

She fusses over her boys (James, 36, and David, 32, are devoted to her), loves a charity shop designer bargain, a joke and a glass of white wine. Only sometimes, when she goes quiet, do you get a sense of the torment within.

To this day she maintains that she never believed Richard deserved to die. She took a life, which she accepts no one has the right to do, no matter how monstrous the victim's behaviour.

The Ferrari-driving car salesman at an event in 2002

Ask if she feels like a murderer or a victim, and she simply shakes her head sadly: 'I just wish it hadn't happened,' she says, her eyes filling with tears.

While Richard would become a successful businessman, it was Sally who had a more prosperous background.

She was born into a very upper-middle class family in Walton-on-Thames — a late-life surprise, and only daughter, when her mother was 44.

Her father, born in India, had studied at Sandhurst and Cambridge and was a brigadier in the Royal Engineers.

Her mother, also born in India, had servants — and a hauteur that followed her to the English suburbs. 'She used to tell us how one year the local maharajah sent her a baby elephant as a birthday present,' says Sally.

Her father died when she was six, and with her much older brothers at boarding school, Sally became her mother's 'project'.

Secretarial college and a suitable marriage were the only available options until one day, when she was 15, Sally met the dashing, 21-year-old Richard Challen.

'I was working on Saturdays in a newsagents and Richard came in and we got chatting. I thought he was so sophisticated. He worked at a car showroom in Surbiton and he'd wear a brown three-piece suit.

'He was exciting and I'd never met anyone like him. We'd drive up to the King's Road in Chelsea in his Ford Anglia for a cup of coffee. My mother was a snob and did not think Richard was 'our sort'.' Her brothers were equally appalled.

From a modern perspective, you could argue that Richard groomed the naive teenager — a child — impressing her with his worldliness but also slowly eroding her confidence and independence.

In an effort to get Sally away from Richard, she was sent to finishing school in Brussels for several months. But the couple stayed in contact by letter and phone, and the relationship picked up as soon as she came home.

Having left school, she got a local secretarial job, and would go to Richard's flat every night to cook his dinner and do his cleaning.

At 17, having had no sex education and with Richard not having instigated contraception either, the inevitable happened; she became pregnant.

Sally says her mother was horrified. When her brothers confronted Richard, he commented: 'Well I wasn't the first.' It wasn't true.

'I didn't think Richard would like it [the prospect of having a baby] so an abortion was the only option,' says Sally.

Even at the outset, she knew he had a wandering eye, yet with no other experience of men, Sally had no template for what a healthy relationship should look like.

'I just thought the way he treated me was normal. I didn't know any better. I was always trying to please him because I thought if I didn't, he'd leave me.'

Once, in her 20s, she confronted him about a particular 'bit on the side' but he threatened: 'Don't make me choose because I'll choose her.'

Sally became hysterical and Richard roughly dragged her down the stairs of his flat, and threw her out in the street. It was an indication of the violence he might be capable of.

Sally today

Yet Sally never once thought she deserved more. 'He was my better,' she says simply. 'Richard was good looking, charming and attentive when he wanted to be.

'He was very popular. I felt he was a catch.' But what about Richard's feelings for Sally?

With so many other 'options' available to him why couldn't he let her find someone else?

Sally believes Richard did love her, but loved the way they were perceived as a couple more. For they did make a striking pair.

Sally with her long blonde hair, compliant, adoring manner and 'nice' accent was just the sort of wife an ambitious, lower-middle class lad 'on the up' would want.

'Whenever he bought me a present, it wasn't to make me happy, it was to show the world how generous he was,' she says. She toys with a chunky, obviously expensive gold necklace he bought her which she still wears.

The couple married in 1979. 'On the day of my wedding, my mother said, 'You don't have to marry him, you know.' Sally just thought she was being a snob.

After the wedding, Richard expected Sally to do all the housework, cooking and washing, even though she also had a full-time job with the Police Federation.

His business was also doing well, and with his good looks and charm, Richard was a brilliant salesman. He had a Ferrari and expensive suits. Sally was always immaculately dressed and coiffed.

But despite working, she had no financial independence. 'I gave Richard my salary. He gave me cash to do the shopping with. That was the way he worked. We didn't have a joint bank account.'

When the boys were born, the entire workload of child-rearing fell to Sally. She still strived to please Richard: the undercurrent of fear that he would leave her was always there.

Sex was always on Richard's terms. Sally would know her wifely services were required when she was ordered upstairs to 'get ready'. 'That meant to go and get clean and put on some decent underwear,' she says with an embarrassed grimace.

'I didn't like to show my body because he said I had one breast bigger than the other and that my nipples were like cigar butts.'

He didn't keep his harsh critiques of his wife private, either. Friends would recall him chiding her about her 'thunder thighs', and asking for comments on the 'size of her a***'.

It was during a trip to America in 1998, when the boys were 15 and 11, that Richard first used sexual violence to 'teach her a lesson'.

They were saying goodnight to friends with whom they were staying one evening when — probably after a glass too many — an old friend kissed Sally forcefully on the lips.

Richard was furious. 'It all happened so quickly,' says Sally. 'Richard took me in the bedroom, bent me over the bed and raped me.

'I couldn't call out, I couldn't say anything, the boys were asleep next door. I spent the night curled up against the wall. I didn't sleep. The next morning he got up, took the kids out for breakfast and left me there.' Sally was terrified. 'He'd never been sexually violent towards me before. I didn't know what was going to happen next. I felt degraded and unclean.'

Fearing further violence, for the rest of her marriage Sally reluctantly let him perform sex acts she didn't want to do.

Meanwhile, having become aware that Richard was cheating on her when the boys were still very young, she became a determined — obsessive the court would later hear — detective as a result. She'd hack email accounts and phone records, and scrutinise receipts.

She found out about the brothel after finding a recurrent number on his phone and calling it.

After the confrontation in which he denied having been there, a difficult Christmas followed with Richard eating on his own the meals his wife cooked, and freezing her out. Weeks later, he announced: 'If things don't go back to normal, I'm going to leave.'

Sally caved in and begged him to stay. She'd wanted him to admit his mistakes and resolve to be a better husband, not leave her.

'I always hoped he would change,' she says. 'I thought that if I confronted him with his lies and did it in a way that he couldn't get out of, he would have to change and we could go back to being happy.'

But, as ever, it was Richard who set the rules. As well as the cheating, name-calling, physical and mental abuse, Richard was also trying to convince Sally that she was going mad.

Sometimes, if she left her car keys out, he would take the car to make her think it had been stolen or replace it with an entirely different one.

Sally found stubs to the London Eye in Richard's coat pocket and when she asked him about it, he accused her of planting them there herself 'because you're mad'. 'I used to think I was going mad, and ask myself, 'How can I prove anything? Am I reading too much into this?'

Early in 2009, Sally had had enough, after seeing a news item where the brothel he had been to was raided and the police found the girls had been trafficked.

She'd started and stopped divorce proceedings five times —but this time she was serious.

They were on a family holiday in Malta when she blurted out: 'I don't love you any more. I want a divorce. He said: 'Well, you know you won't get anything.'

'That was his reaction. He didn't say, 'please don't leave me, I love you'. At first, I was euphoric, thinking, 'I can start a new life'.'

She left Richard, bought a house nearby (with money inherited from her mother) and moved in with her younger son David who was, by now, in his early 20s and fully aware of his father's shortcomings.

James stayed with Richard for a while, before moving out himself. It didn't last. 'I absolutely hated it,' says Sally. 'I couldn't sleep, I was on my own. I couldn't cope without him.'

That may seem strange given the horrors she'd endured, but Richard had defined her whole adult life. He was all she knew.

In one email, sent on April 6, 2010, she wrote: 'I want to be with you, I am sorry I left. We are soulmates, we have been together so long, I can't see a future without you. You are my life, I love you.'

Richard replied: 'I will consider your return only on these terms . . . when we go out together it means together. This constant talking to strangers is rude and inconsiderate. We will agree to items in the home together. To give up smoking. To give up your constant interruptions when I am speaking.'

He also insisted that in any future divorce her settlement would be £200,000 — a fraction of what she was entitled to. Sally promised to obey all the rules.

On August 13, 2010, the day before she killed Richard, Sally went to a lawyer in Kingston upon Thames to go through the post-nuptial agreement.

The solicitor thought it was a terrible idea, but Sally ignored her. To mark their reconciliation, she and Richard were planning a six-month trip to Australia together.

The following day, she visited Richard at the marital home. They were clearing it out with a view to letting it while they were abroad. 'He announced he wanted a cooked breakfast even though it was the afternoon,' says Sally.

'Sausage, egg and bacon. But he didn't have anything in the house, so it meant going to Somerfield. It was pouring down, but even so, I was expected to go to the shops, which I did. I felt he wanted me out of the house and the breakfast was an excuse.'

When Sally returned just after 3pm, Richard was upstairs getting dressed. 'I noticed that the phone handset was now on the sofa — it hadn't been when I left — so I dialled 1471.'

Sally had a set of keys to the marital home and had been coming in and clandestinely checking his online activity and emails. She recognised the number as belonging to a woman Richard had met on a dating website.

Nothing had changed. Richard hadn't changed. 'I cooked the meal. He was upstairs on the computer. As soon as I went upstairs, he blanked the screen.

'Then Richard came downstairs, sat down and I put his meal in front of him and I said, 'Am I going to see you tomorrow?'

'He said, 'Don't question me, Sally, don't question me'.

'And it was the way he said it, and it was what he used to say to me always, 'Don't question me, because you're not going to get an answer, so don't even bother going there.' And that was it . . . I just flipped.'

Sally had brought a hammer with her to the house in her handbag — something the prosecution leaned on heavily during her trial.

'When I moved out of the marital home someone had put together a toolbox for me so I would have one at the new house and it was the hammer in there,' she explains.

Today, Sally swears she has no memory of putting it in her bag. 'Although I must have done, because it was there, it was in my handbag.'

Then came the horrifying moment that changed her life for ever and ended her husband's.

'I went behind him as he sat at the table, eating his meal. I picked the hammer up and hit him over the head with it. I hit him and I hit him and hit him and hit him.

'It was like an out-of-body experience, it wasn't me doing it. I'd never hit him before. I'd never hit anyone before in my life — I don't remember smacking James or David ever.

'The prosecution say I hit him 18 times, which seems like a ridiculous amount. I can't believe that — it didn't feel like that.

'It felt like I was on some sort of autopilot. Richard was on the floor. I knew that he was dead because I felt his skin. He wasn't breathing. I rubbed his leg.

'Then I went through to the garage and found some old blankets. I brought them over and I covered him up. I didn't want David or anyone to find him like that, to see that . . . I wrote on a piece of paper: 'I love you, Sally,' and placed it on his body.'

The scene in the kitchen must have been gruesome and Sally spattered with blood, but she says she has blanked it out.

Tellingly, though, she says she remembers taking her socks off to walk upstairs and she also went looking for clothes to change into (hers were in her own home.)

'I put on a pair of old trousers I found in David's wardrobe — one of Richard's jumpers and a pair of his socks. I looked in the mirror in our en suite and I remember seeing a spot of blood on my forehead. I stared at it. But it was as though I was totally detached from this.'

Then she locked the door and drove home . . .

As we'll discover on Monday, while Sally was finally free from her tormenter, her inner torment was greater than ever and she felt there was only one terrible option now open to her.

ON MONDAY: I drove to Beachy Head to end it all