A medical student is among four men being questioned by counter-terror police on suspicion of being involved in a potentially "significant" Islamist terrorism plot.
One of the suspected extremists is understood to be 21-year-old Tarik Hassane, who lives near Ladbroke Grove in west London.
At least one of the suspects is believed to have travelled to Syria and one line of inquiry is to establish any possible links with Islamic State (IS), the extremist group behind the beheading of British aid worker Alan Henning.
Hassane and three others, aged 20 to 21, were arrested on Tuesday in a series of raids at addresses across London.
The front door of Hassane's property showed signs of forced entry and has been boarded up.
Counter-terror officers believe the raids were an "early disruption" of what could have turned into a "significant plot".