Both are due to be sentenced on 23 March.
Traffic commissioner Nick Denton, commenting on the case, said it showed “horrifying negligence and irresponsibility”.
On 26 August last year, Ryszard Masierak stopped his HGV in lane one of the M1, near Newport Pagnell, where he remained for more than 12 minutes. A minibus approached and stopped behind the truck, unable to pull out because of traffic in lane two.
A second HGV then approached the two vehicles, driven by David Wagstaff who had the vehicle on cruise control and was using his mobile phone on handsfree. He collided with the stationary vehicles, while travelling at 56mph, pushing the minibus under Masierak’s lorry.
Eight people died at the scene: seven of the minibus passengers and the minibus driver.
Masierak was breathalysed and found to be over the prescribed limited. Both HGV drivers were arrested and charged.
“This incident, caused by driver error of one drink driver and the prolonged inattention of another, resulted in a tragic waste of life and could have been avoided,” said Louise Attrill, senior crown prosecutor for Thames and Chiltern Crown Prosecution Service.
West Midlands traffic commissioner Nick Denton said: “Professional HGV drivers must constantly show through their driving behaviour that they are fit to be given charge of a truck weighing up to 44 tonnes. Most HGV drivers do. But through his horrifying negligence and irresponsibility, Mr Masierak has shown that he is utterly unfit to be entrusted with the right to drive HGVs.
“Rules on driving time and drink driving are there for good reasons but Mr Masierak ignored them, with catastrophic consequences for the innocent victims and their families.
“Mr Masierak’s right to drive HGVs has been revoked and if he ever intends to re-enter this profession, he will face a nigh-on insuperable challenge persuading a traffic commissioner to return that right to him in the face of his actions.”