Some 11 people "will be interviewed as witnesses" by the police searching for missing Madeleine McCann, Good Morning Britain heard.
British and Portuguese "men and women" are expected to be quizzed by the police over what happened to the missing youngster.
Four men arrested in connection with an alleged Islamist terror plot just two days before Remembrance Sunday will be held for a further seven days.
Counter-terror police detained the men, aged 19 to 27, on Thursday night at locations across west London and High Wycombe in the Thames Valley area, Scotland Yard said.
Several properties across the south east of England are being searched as part of an ongoing investigation into Islamist-related terrorism.
Four men remain in custody after being held overnight during raids across Thames Valley and west London in relation to an alleged terror plot.
One of the men, a 19-year-old arrested at an address in High Wycombe, has been named locally as Yousaf Syed.
His friend told ITV News he was a "really nice guy" and accused officers of "demonising" the Muslim community.
ITV News UK Editor Rohit Kachroo reports from High Wycombe:
A 19-year-old man arrested at an address in High Wycombe by counter-terrorism officers is Yousaf Syed, ITV News understands.
He was one of four men arrested across Thames Valley and west London overnight in relation to an alleged Islamist terror plot.
Eight addresses across Thames Valley and west London are being searched as part of an ongoing investigation into Islamist-related terrorism, Scotland Yard has said.
Searches are taking place at three properties in High Wycombe along with addresses in Greenford, Hounslow, Hayes, Southall and Uxbridge.
Police confirmed four men arrested overnight in relation to an alleged Islamist terror plot remain in custody pending further enquiries.
The Metropolitan Police statement confirmed officers from Counter Terrorism Command were "working closely" with their colleagues in SE Counter Terrorism Unit and MI5.
A window pane at the door of one of the properties in High Wycombe searched by counter-terror police has been seen cracked after the initial raid.
Four men were held in Thames Valley and west London in connection with an alleged Islamist terror plot.
Properties in High Wycombe and west London have been searched after the arrest of four men in connection with an alleged Islamist terror plot.
Police vehicles and tape were seen outside two addresses in High Wycombe, in Desborough Avenue and West Wycombe Road.
It is understood police believe the arrested men were plotting an attack on British soil.
The Metropolitan Police said the arrests and searches were part of an "ongoing investigation into Islamist-related terrorism".
Counter-terror police have arrested four men in relation to an alleged Islamist terror plot, Scotland Yard has said.
Three men, aged 22, 19 and 25, were arrested after Metropolitan Police's Counter Terrorism Command executed warrants at addresses in west London and Thames Valley, while a 27-year-old man was arrested in the street in west London by armed officers.
All four were taken to police stations in central London and remain in custody. They are held on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism.
Two of the entries to premises were assisted by firearms officers but no shots were fired.
A number of residential addresses and vehicles are being searched by specialist officers in west London and Thames Valley as part of the investigation.
The Metropolitan Police is to pay over £400,000 in compensation to a woman who had a child with an undercover officer.Read the full story ›
Investigators have been searching the home of a Royal Protection officer and a police building in the grounds of Buckingham Palace where ammunition was found.
Today's arrest came about as a result of an internal investigation by the Metropolitan Police.
The investigation, by the Directorate of Professional Standards, commenced a few weeks ago following the reporting by officers from Royalty Protection of ammunition found in their personal lockers or belongings.
Assistant Commissioner Mark Rowley said a reorganisation of the force's Protection Command had "revealed a few pockets of poor behaviour".