The pair was allegedly in breach of a travel ban that means that are not allowed to leave the UK without permission.
It will fuel concerns that the men may have been trying to cross Europe and get in to Syria.
Keeler, 44, was acquitted in July of planning to travel to Syria to join ISIS after he was discovered in the back of a lorry at the sea port of Dover. However, he was jailed for 15 months after admitting possession of false identity documents, meaning he has allegedly fled the UK just after being released from prison. Brooks, 40, found notoriety in 2006 after heckling a speech by Great Britain’s then Home Secretary John Reid.
In 2008 Brooks and Keeler were jailed for four and a half years after being convicted of inciting terrorism abroad and terrorist fundraising. The sentences were later reduced on appeal. Following their release, both men were made subject to travel restrictions which meant they had to seek permission to travel abroad.
Jamaican-born Brooks converted to Islam at the age of 18 and soon came under the influence of notorious hate cleric Abu Hamza, who is currently serving a life sentence in the United States. He later visited Afghanistan and Pakistan, where he allegedly received terrorist training. He was a preacher of Al Ghurabaa, an organisation banned in 2006 for terrorist connections.
A Scotland Yard spokeswoman said: “On Sunday, 15 November officers from the Met’s Counter Terrorism Command (SO15) were informed that two UK nationals had been detained in Hungary. “After further enquiries, UK officers applied for arrest warrants for both men for breaches of notification requirements under Part 4 of the Counter-Terrorism Act 2008, which were granted at Westminster Magistrates’ Court on Monday, 16 November. Enquiries continue”, the official said.
Police in Hungary said the two men were on a train heading for Bucharest, the Romanian capital, when they were stopped for identification at the border station of Lőkösháza. Keeler had a valid British driver’s license, while Brooks gave police a copy of the Koran when asked for identification, sources said.
They stressed the investigation was not linked to the Paris attacks and face deportation back to the UK.