Judge Mr Justice Stuart-Smith gave no indication on what sentence would be given to either Festus or Fiona Onasanya.
After the verdicts were returned, Mr Justice Stuart-Smith, said: “This is not going to be easy, not to give any indication one way or the other.
“What your client should understand, although she knows the seriousness of this, I will listen to all considerations.”
Onasanya gave no visible reaction to the unanimous verdict in court and did not comment to the Press.
Following the verdict, a spokesman for Cambridgeshire police said: “We will continue to investigate those who think it is acceptable to try and evade the law in relation to motoring offences, working closely with the CPS to ensure those responsible are prosecuted.”
Donna Rayner, of the CPS, said: “Fiona Onasanya and her brother Festus both lied to the authorities in the hope they could avoid the consequences of their speeding offences.
“Fiona Onsanya denied perverting the course of justice but the CPS presented evidence that her phone was in the area when the speeding took place and the man she had nominated as the driver was, in fact, out of the country. Clearly the jury did not believe her explanation.”