Essex Police involved in coach and bus spot-checks found two Polish drivers without legal documents and they were immediately taken off the road.
Replacement drivers had to be sent by the Midlands-based operator and passengers were forced to wait several hours.
Both Polish drivers were also alleged to have exceeded tachograph hours. The checks were part of Operation Tourist, a safety crackdown.
Of 23 vehicles stopped by Essex Police only 11 were problem free and 24 offences were discovered.
One driver was arrested because of an outstanding warrant following previous driving allegations.
Another six drivers were found to have committed tachograph offences.
Six vehicles were issued with delayed prohibition notices in respect of minor defects. This means they were able to continue after being given a deadline for the defects to be rectified.
An Essex Police spokesman said: "We regret any inconvenience to passengers but hope they will accept that Operation Tourist was organised with their safety in mind.
"The problems detected show that such spot- checks on coaches and other heavy goods vehicles are necessary to try to prevent death and injury on the road."
Last year a similar operation saw 30 coaches or buses stopped by Essex Police.
Three had serious defects and were immediately banned and three drivers were given delayed prohibition notices for minor defects. Seventeen drivers were found to have worked excessive hours.
Saturday's checks were carried out on the M25 at the Thurrock Service Station and police were joined by the Vehicle Inspectorate.
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