Second man arrested in connection with Parsons Green attack
The 21-year-old was detained in Hounslow, west London on Saturday night
On Saturday morning, Kent Police arrested an 18-year-old man in Dover
UK terror threat level reduced from 'critical' to 'severe'
Police 'keeping an open mind' on number of suspects involved
Of the 30 people injured, one is still being treated in hospital
Police have again appealed for anyone with footage and images from the attack to pass them to investigators.
They can be uploaded at .
Anyone with information is urged to call the Anti-Terrorist Hotline on 0800 789 321.
Home Secretary Amber Rudd says the government will this week advertise for the newly-created role of .
The job will have a remit to "identify extremism and advise the government on new policies, laws and other actions that may be required to tackle it".
A 13-year-old schoolboy has described being trampled in a stampede as passengers fled from the attack on Friday.
Alex Ojeda-Sierra told : "One man fell on me and my legs bent backwards and my right ankle got twisted. I started screaming that I had no air."
Alex was treated at Chelsea and Westminster hospital and is now at home recovering.
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Our home affairs correspondent Dominic Casciani is at the scene in Sunbury-on-Thames:
Quote MessageResidents living close to the property at the centre of the Parsons Green investigation say the search currently underway appears to be very extensive. A police forensics tent is now in place in the back garden of the property belonging to Ronald and Penelope Jones and large numbers of officers have been working inside. Police dogs at the scene appear to be one of the breeds trained to search for explosives and chemicals. Some residents have been told by officers that the outer cordon which is limiting access to a number of neighbouring roads will be lifted by early afternoon but that the inner cordon surrounding the Cavendish Road property will remain for some time. There has been no formal confirmation from the Metropolitan Police."
Image source, Getty Imagesthat one person remains in hospital following Friday's attack.
In total, 30 people were received by hospitals, 19 of whom were taken by ambulance.
The remaining patient is at Chelsea and Westminster hospital, where the majority of victims were treated.
Police have put up barriers on a street in Sunbury-on-Thames.
They are searching what's believed to be the home of the 18-year-old suspect arrested on Saturday morning.
Shadow Home Secretary Diane Abbott earlier told the ´óÏó´«Ã½ of her concerns about police resources amid a rise in terrorist attacks.
She said: "It is the fifth attack and it is concerning. There are issues about resources and the sustainability of person power when it comes to responding to these attacks."
Ms Abbott also urged the public to remain calm when they return to work and school on Monday.
"The point is people should be alert but they should not be alarmed because that's what the terrorists want to do, they want to scare and disrupt our society."
Police are searching a house in Sunbury-on-Thames - believed to be the home of the 18-year-old-suspect arrested in Dover on Saturday.
Barriers have been put up around the house.
Image source, ReutersOur correspondent Kathryn Stanczyszyn is in Sunbury-on-Thames and says that activity is "ramping up".
Police began searching a property in Cavendish Road on Saturday, believed to be the home of a man arrested in Dover on Saturday morning.
She says there has been intense activity overnight, and a perimeter erected in the past hour.
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Ms Rudd claims the police can make savings to fund a 2% pay rise without cutting jobs.
She says: "They have £1.5bn in reserves and Tom Winsor [Chief Inspector of Constabulary for England and Wales] has been quite clear from his report that there are additional savings police can make."
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Ms Rudd says she accepts there are 23,000 fewer police officers compared to 2010. However, she says that between 2010 and 2015 crime came down.
It is "too simple" to say that as police numbers have fallen terrorist attacks have risen, says Ms Rudd.
"What we have is an onslaught of attack from Daesh trying to radicalise people. We have to work against making sure that foreign fighters don't come back here from Syria," she says.
Amber Rudd says the second arrest in the Parsons Green investigation suggests the attacker was not "a lone wolf" - but she added it was "too early to reach any final conclusions".
Amber Rudd: Second arrests suggests 'not a lone wolf'
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Ms Rudd says the government is "absolutely committed to making sure the security services and the police have the right resources".
She says: "Today we have announced £24m of new money which will go to counter-terrorism operations across the country where it's needed, particularly to support operations where they're protecting people in public."
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So-called Islamic State has said it was behind the Parsons Green attack.
But Ms Rudd says: "It is inevitable that so-called Islamic State or Daesh will reach in and claim responsibility. We have no evidence to suggest that yet.
"But as this unfolds and as we do our investigations, we will make sure we find out how he was radicalised if we can."
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Home Secretary Amber Rudd tells The Andrew Marr Show it is "too early to say" whether the 18-year old arrested on Saturday in Dover was acting as a "lone wolf".
But she says the second arrest "suggests" the attacker was not working alone.
"This has been a year like no other," she says about the five terrorist attacks in 2017 - as well as six attempts foiled by the police.
The British Transport Police firearms unit has placed extra officers on duty and they will be patrolling stations again on Sunday:
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Image source, PAOur correspondent Andy Moore is at Sunbury-on-Thames where police are continuing to search a home.
It is thought the 18-year old man arrested in Dover on Saturday morning lives there with his foster parents.
Our correspondent says that overnight, a barrier was erected in front of the property - which "suggests that they intend to be at this house for some time".