Two men being questioned by police in relation to the bombing at Parsons Green station were reportedly fostered by the same couple.
An 18-year-old and a 21-year-old have been arrested under the Terrorism Act on suspicion of being involved in the explosion on Friday, which injured 30 people.
The former is believed to be an orphan from Iraq.
Both are thought to have spent some time being cared for by Ronald and Penelope Jones, who had previously been granted MBEs for services to families and children.
The couple’s residence was subjected to an armed raid on Saturday and is still being examined by counter-terror personnel.
The UK terror threat level has been lowered from its highest point of ‘critical’, meaning an attack was imminently expected.
The Joint Terrorism Analysis Centre’s lowering to the ‘severe’ level suggests a continued threat from any alleged networks was not present anymore.