It comes after viral footage online showed far-right activist Tommy Robinson walking by a guy lying on the ground at the station shouting, “he come at me”.
Police were called to St Pancras on Monday (July 28) just after 8.40pm to reports of an assault.
A man was taken to hospital with serious injuries, which since are not thought to be life threatening.
Following the incident, British Transport Police (BTP) said that the suspect fled the country.
Officers have arrested a 42-year-old man from Bedfordshire on suspicion of grievous bodily harm.
He will be taken into custody for questioning.
The arrest was at Luton Airport shortly after 6.30pm, after officers were notified that the suspect had boarded an incoming flight from Faro.
BTP said the man had been wanted for questioning after leaving the country to Tenerife in the early hours of August 29.
In one video at St Pancras, Robinson was seen walking past a man on the floor.
In another video, Robinson had also filmed himself that day while walking in the station.
He was then seen boarding an airport shuttle in Tenerife.
A BTP spokesperson said: “The arrest took place at Luton Airport shortly after 6.30pm, following a notification that the man had boarded an incoming flight from Faro.
“The man had been wanted for questioning after leaving the country to Tenerife in the early hours of 29 August following the incident at St Pancras.
“He was arrested on suspicion of GBH (Grievous Bodily Harm) and will now be taken to custody for questioning.”
