A man from Hertfordshire has been arrested at Gatwick Airport on suspicion of preparing terrorist acts.
The 44-year-old was getting off a flight from Iraq yesterday when he was met by anti-terrorism officers.
He was then taken to a central London police station where he remains in custody.
The arrest comes on the same day that a 31-year-old man from Norfolk was held on suspicion of fundraising for terrorism purposes and supporting a banned terror group.
A 31-year-old man arrested in Norfolk on suspicion of terror offences has been released on bail.
Officers from Scotland Yard's counter terrorism team arrested him on Thursday morning.
The man is suspected of fundraising for terrorism purposes and supporting a banned terror group.
Police are searching two addresses in Norfolk and one in London. The Metropolitan Police said the offences related to activities abroad.
A hospital in Cambridge will carry out a live exercise later to prepare for a surge in casualties in the event of a terrorist attack.
Addenbrooke's has previously run exercises on how to deal with an Ebola outbreak and cyber attack.
A 38-year-old man has been arrested in Luton as part of a "large scale fraud" investigation linked to UK extremists travelling to Syria.
He was one of seven people - six men and one woman - detained as part of the operation.
Six of the arrests were made in London after six properties were raided by counter-terrorism officers from the Metropolitan Police.
The Luton man is being held on suspicion of conspiracy to commit fraud and money-laundering.
The arrests are linked to allegations that vulnerable and elderly people were cold-called on their home phones by someone impersonating a police officer.
Two people have been arrested in Essex in connection with suspected terrorism in Syria.
Police say they arrested a 37-year-old man and a 36-year-old woman on Wednesday, on suspicion of "being involved in the commission, preparation and instigation" of terrorism. They have been taken to a police station in London for questioning.
Officers made the arrests as part of a series of searches at various UK locations. Scotland Yard said: "The searches are ongoing and we are unable to provide more details at this stage.
The Luton terrorist group were trying to make an an improvised explosive device (IED) based on instructions in an al Qaida manual entitled "Make a bomb in the kitchen of your mom - by the al Qaida chef", the court was told.
Covert recordings of the pair heard Iqbal suggesting attaching the bomb to a remote controlled toy car and sending it under the gap of a gate to a Territorial Army (TA) centre in Luton.
The men were arrested following a series of raids at their homes in April last year after an intelligence-led joint operation by the Metropolitan Police Counter Terrorism Command and the British Security Service (BSS).
A Territirial Army centre in Luton was the planned target for a terror group. Four men have admitted engaging in conduct in preparation for acts of terrorism.
Four Luton men could be sentenced today after admitting discussing carrying out a terror attack in the UK.
Zahid Iqbal, 31, Mohammed Sharfaraz Ahmed, 25, Umar Arshad, 24, and Syed Farhan Hussain, 21, considered methods, materials and targets for an attack.
The men were arrested following a series of raids in April last year. They pleaded guilty to one terrorism charge at Woolwich Crown Court.
The four men downloaded computer files containing practical instruction for an attack, and collected funds for terrorist purposes.
They also admitted facilitating, planning and encouraging travel overseas, as well as organising, encouraging and participating in physical training, contrary to section 5 of the Terrorist Act 2006.
The offences took place between January 2011 and April last year.