Rail passengers were searched for drugs as they arrived into town on Friday evening.
Officers used specialist police dogs to search people as the arrived at Sutton station and found 10 people with cannabis and a further person carrying a class A drug as well as cannabis.
The police dogs identified 26 suspects and even those who were not carrying drugs at the time admitted having drugs on them earlier, according to Sergeant Simon Alexander.
Inspector Richard Hall said: "Anyone bringing drugs into the town centre can expect to be stopped and dealt with robustly.
"Further operations are planned."