Labour whip Fiona Onasanya, 35, was found guilty of perverting the course of justice at the Old Bailey today

As a Labour whip, Fiona Onasanya was responsible for ensuring the discipline and loyalty of her fellow MPs.

So how ironic that what ultimately sealed her fate was a fatal blow delivered by of one of her closest political allies.

It was only after her first trial had begun that prosecutors were handed the key piece of evidence that finally nailed the 35-year-old's lies.

Reading details in his local paper, Dr Christian DeFeo, her former aide, realised the speeding offence which put her in the Old Bailey dock had taken place close to his home on a night when she had driven to visit him.

Onasanya had denied being behind the wheel of the Nissan Micra when it was clocked at 41mph in a 30mph zone. Instead it was claimed that a Russian man was driving.

But in his bombshell evidence Dr DeFeo described how the MP had in fact arrived, alone, in the car, and had spent at least two hours at the property, leaving so late his wife had offered her a bed for the night.

He also told the court he had never seen anyone but Onasanya behind the wheel of her Micra and that two mobile phones which police said were in the car at the time of the offence belonged to her and were never out of her sight.

While Onasanya would take the stand and try to claim that her former speech writer had got it wrong, no one was in any doubt as to the significance of his intervention – Dr DeFeo included.

'It is with the greatest reluctance I have to do this,' he told the Old Bailey. 'But to do otherwise, I cannot. It is legally and morally unacceptable not to.'

And therein lies a second irony. Because when it comes to morals, Onasanya has made a great play of hers ever since her election.

Ms Onasanya was accused by prosecutors of telling the court 'a dishonest construction put together from top to bottom with lies'

Her conviction was secured after testimony from former aide Christian DeFeo, pictured here with Onasanya

When questioned by police over the speed of her Nissan Micra in this speed camera photograph - and over her confused and confusing written answers to their questions - Onasanya remained completely silent

In interview after interview the qualified solicitor told how her Christian upbringing had moulded her into the person she was, encouraging her to go into law because she wanted to 'help people'.

'I am motivated in all that I do by my abiding faith in God,' she said in her maiden speech to Parliament. She ended her address with the words: 'I intend to do right.'

Thus far that has largely meant showing unswerving loyalty to Jeremy Corbyn, whom she gushingly praised as a 'visionary' and the architect of a 'new and better way'.

Yet what ultimately brought Onasanya down was the old sin behind the demise of so many politicians through the ages – hubris, the arrogance and pride that so often precedes a fall.

Accused of a minor motoring offence she decided that, rather than face the rap, she would wriggle out of it, enlisting her brother's help.

'This case may have started as a case about an offence of speeding,' said David Jeremy QC, prosecuting.

'It has become, as a result of the choices made by Miss Onasanya, a case about lying ... lying to avoid prosecution for a breach of the laws that apply, or should apply, to every single one of us whoever you may be. What a shame she did not tell the truth in the beginning.'

While not the first politician caught out by lies – the former Lib Dem minister Chris Huhne was jailed in remarkably similar circumstances – what is extraordinary about Onasanya's case is the trajectory of her rise and fall.

'I am motivated in all that I do by my abiding faith in God,' the newly-elected MP said in her maiden speech to Parliament

This was a woman who, until she was elected as MP for Peterborough in June last year, was unheard of in national politics.

And yet within months she had been chosen as a Labour whip and was tipping herself to become the UK's first black woman prime minister.

So what is known of her?

Her mother Paulina was born in London but met her father, Frank, in Nigeria before they settled in Cambridge, where he played semi-professional football.

Onasanya and her younger brother Festus – they are just 16 months apart – were born and grew up in the city, although her parents' marriage broke up when she was three.

When she was injured as a child following a collision with a speeding car, her deeply religious mother took her home and prayed.

The MP went to the Netherhall co-ed state school, leaving with 11 GCSEs and four A-levels, 'mostly Bs'.

After that she decided to study law at the University of Hertfordshire, qualifying as a solicitor in 2015.

Within months of her election win, loyal Corbynite Onasanya had been chosen as a Labour whip and was tipping herself to become the UK's first black woman prime minister

She chose commercial property law as it was the least 'contentious', saying other areas, such as the criminal law, didn't always have a 'happy ending'.

'I wouldn't want to send someone innocent to prison, or vice versa try and negotiate terms for someone that maybe should go to prison,' she observed.

Given her current predicament, those are skills that might have come in handy.

She claims she entered politics by accident. In 2011 she was with a friend in a pub talking about the London riots when the secretary for the Cambridge Labour Party overheard her and asked her to join them.

She did so and in 2013 was elected as a Labour county councillor, before rising to deputy leader of the Labour group on the council. In 2017 she was selected as Labour's parliamentary candidate for Peterborough.

It was a tough seat. The Tory incumbent, Stewart Jackson, had been in situ for 12 years and UKIP did not stand because it wanted to give Eurosceptic Mr Jackson a better chance of winning.

Indeed it was only following a recount that at 3am on the morning of June 9 that Onasanya was announced the victor with a majority of just 607 votes.

Quite an achievement.

And yet, within weeks, the seeds of her downfall would be sown.

On July 24, 2017, at 10.03pm a speed camera on the B1167 at Thorney flashed into action, capturing the MP's speeding car.

As automatically happens in such cases, a week later a notice of intended prosecution (NIP) form was sent to Onasanya. It was duly returned naming a Russian man called Aleks Antipow as being behind the wheel. Mr Antipow had previously lived in Chesterton, Cambridge, at a house rented by Onasanya and her brother, the court heard.

In July, Fiona Onasanya and her brother Festus, 33, pictured above, were charged with perverting the course of justice. He pleaded guilty. At her trial she tried to place all the blame for the matter on him, telling the Old Bailey he had 'set her up'

Initial enquiries by police found that the form contained incorrect details for Mr Antipow. Another letter asking for them to be checked was sent to the MP on September 14.

Onasanya replied a week later: 'I am not sure how I can be of further assistance. I have supplied the details made known to me as well as the licence information. It is a criminal offence to say I was the driver when I was not.'

She would subsequently be forced to admit she had not in fact filled in the original NIP form. Her explanation was as follows. Onasanya claimed that she had left the form for her mother to deal with, believing that because the offence was committed on a Monday she would have been staying in London to attend to her normal Parliamentary duties.

The car would have been left in Cambridge, so that her mother, brother or others could drive it.

But, she claimed, her assumption about the timing of the speeding offence was wrong: Parliament had in fact gone into summer recess the previous week. That meant she had not been in London on the day in question. An honest mistake of a busy woman, she said. She only realised she had got the wrong date when she was charged by police – a full year after the incident. She had checked her diary and realised her mistake.

Onasanya told the court that when she had sought further details about the case back in September 2017, she had been assured by her brother that 'it was sorted out'. Apparently satisfied with that explanation, she asked no further questions.

She went on to explain this staggering lack of curiosity by claiming that at the time she was very busy in her new job. And she claimed she was 'not in a good place', due to health issues relating to an earlier diagnosis of multiple sclerosis.

When the police's attempts to find Mr Antipow hit a brick wall they once again asked the MP for clarification by email and letter.

Onasanya left the Old Bailey today aware she might face a prison sentence. In 2013 Liberal Democrat MP Chris Huhne and his ex-wife Vicky Price were both jailed for eight months for a very similar offence

She claimed that Mr Antipow had filled in the NIP form himself. Inquiries would establish that at the time of the offence he had actually been more than 1,000 miles away at home in Russia.

Officers once again set in motion attempts to contact the MP and were eventually able to schedule a voluntary interview for January 2 this year. During dozens of questions at Bedfordshire Police Headquarters, Onasanya remained completely silent.

In her defence it was claimed that she had a cold on the day, and she felt 'overwhelmed'. In July, Onasanya and her brother were charged with perverting the course of justice. He pleaded guilty.

She later claimed in the dock that Festus had 'set her up', that she was unaware of his criminal behaviour and was shocked when she learned what he had done.

'I haven't spoken to him about why he has done this but I need to,' she told the original trial.

It was the prosecution case Festus and his sister had acted together, co-ordinating their lies. Onasanya denied this was the case, blaming her brother alone.

But in the end her attempt to save her skin by sacrificing her sibling was undone, in large part, by the last-minute intervention of Dr DeFeo.

'The evidence of the DeFeos exposes Ms Onasanya's story as a dishonest construction put together from top to bottom with lies,' said the prosecutor.

With her career – both political and legal – now in ruins, the maniacally busy life of an MP is probably not something she will have to worry about in the future.