More than 30 people were stopped at Kings Cross underground station on Monday to prevent a "potential breach of the peace" at the Notting Hill Carnival.
A Scotland Yard spokesman said: "The group - believed to be around 34 individuals - were stopped at the station at around 3.45pm after it was suspected they were heading to the carnival to commit disorder."
It is believed they had travelled by train from north London.
So far, 15 of the group have been arrested to prevent a breach of the peace.
Hundreds more revellers are flocking to Notting Hill for the carnival's headline day.
The spokesman said they will all be "detained at an appropriate location" until police are satisfied that there is no longer a risk they will commit disorder at carnival.
Police overseeing Europe's biggest street festival were hoping for a peaceful climax to the Notting Hill Carnival despite at least two stabbings.
Hundreds of thousands of revellers were flocking to the capital for the carnival's headline day.
Bank Holiday Monday sees a parade of floats and brightly-dressed performers snake their way through the streets of London as part of the annual Caribbean-inspired celebration.
It was family day at the carnival on Sunday, with young performers lining the streets
Yesterday's festivities were largely peaceful but one 20-year-old man was left in a serious but stable condition after being stabbed in the back and buttocks in Ladbroke Grove.
Metropolitan Police said a 14-year-old boy was slashed with a sharp object in Golborne Gardens.
And a 16-year-old girl was also treated but discharged herself from hospital after sustaining what police described as a superficial leg wound in Wornington Road.
An extra 2,000 police officers will be drafted in to support the event today, bringing the total to 7,000.
Scotland Yard arrested 96 people on Sunday, mainly for drug and public order offences as well as robbery and assault.
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