Peterborough MP Fiona Onasanya has told her trial she waited more than a year before investigating whether she was driving at the time.
Ms Onasanya, 35, allegedly schemed with her brother to claim a Russian man was behind the wheel of her Nissan Micra when it was clocked doing 41mph in a 30mph zone.
Ms Onasanya said she initially believed she was in Westminster on July 24 last year at the time the car was clocked in Thorney, on the basis it was a Monday when Parliament is often sitting.
So, Onasanya said, she left a Notice of Intended Prosecution (Nip) letter at her mother’s address for whoever was driving at the time to reply to.
“When was the first time you started to piece together your movements on July 24,” her lawyer, Christine Agnew QC, asked.
The MP replied: “When the solicitors I instructed in July this year said ‘You need to go over your steps’.”
Onasanya said she believed her brother had been sorting the Nip, and that she had been distracted by Westminster’s heavy workload and ill health.
The MP went on to tell jurors that she suffered a relapse of multiple sclerosis in September last year.
She said: “I probably was not in the best head space. I’ve just been told I had got an incurable degenerative disease.”
Her car was caught by a speed camera on The Causeway, near the Cambridgeshire village of Thorney, at 10.03pm that day and her phones were traced to the area.
The Nip was returned, naming the driver of her car as Aleks Antipow.
But jurors were told that Mr Antipow was at home with his parents in Russia at the time.
He previously lived in Chesterton, Cambridge, at a house rented by Onasanya and her brother Festus, the court heard.
It was also claimed that the contact address and phone number given were linked to Onasanya’s 33-year-old sibling.
Festus Onasanya, of Chesterton, had previously deployed the same tactic, jurors heard, and he pleaded guilty to three charges of perverting the course of justice.
One of those counts related to the July 24 incident.
The MP, who was promoted to the Labour whips office after a rise through national politics, also said she had not been aware that her brother had nine points on his licence and had previously been disqualified for drink-driving.
In July last year, he had nine points on his licence, three short of disqualification limit, and previous convictions for speeding, the court was told.
She is yet to tell jurors where she was at the time of the speeding offence, but said she regularly left her car - which was written off in a later accident - at her mother’s home and permitted others to use it.
The court also heard that, on February 3 last year, Fiona Onasanya had correctly filled out an Nip for triggering another camera a month