Police confirmed that a man in his forties had been taken into custody under the Counter Terrorism and Border Security Act upon returning to the UK from Russia.
British anti-Islam campaigner Tommy Robinson stated he was held at Heathrow Airport on Saturday and had his mobile phone confiscated, following a week in which he extensively shared content online regarding racist and anti-immigrant unrest in Northern Ireland.
"My phone has been taken by law enforcement," he wrote. "Please assist in launching my legal defense fund."
Throughout the past week, Robinson repeatedly posted on social media about riots that erupted in Belfast after a video circulated depicting a brutal knife attack on a man, who lost an eye in the incident.
A Sudanese individual has been charged with attempted murder. Authorities have indicated they are not classifying the assault as an act of terrorism.
In the subsequent days, mobs targeted residences and businesses owned by ethnic minorities or foreign nationals in what Hillary Benn, Northern Ireland's secretary of state, described as racist thuggery.