Video report by ITV News Correspondent Emma Murphy

CCTV footage appearing to show the Parsons Green bomber on his way to carry out the attack after leaving a property at the centre of the police investigation has been obtained by ITV News.

The exclusive footage shows a person leaving the property in Sunbury-on-Thames which has been raided in connection with the London tube train bombing, early on Friday morning.

Police remained at the Surrey property on Sunday as the investigation continued.

Two men are being questioned by police in connection with the bombing. On Monday evening, police were given more time to question the men.

One of those is believed to be 21-year-old Yahyah Farroukh, who was detained at a chicken shop in Hounslow, west London.

On Sunday the UK's terror threat level was downgraded from critical to severe, meaning an attack is highly likely.

The person in the CCTV footage can be seen carrying a Lidl bag at 6.50am on Friday morning.

Just 90 minutes later, at 8.20am a bomb exploded on the District Line train, causing a fireball and injuring 30.

In pictures taken at the scene, the bomb can be seen in what appears to be a Lidl carrier bag.

The Parsons Green tube bomb was in a Lidl carrier bag.

On Saturday morning, police arrested an 18-year-old man in connection with the attack at Dover.

Witnesses described seeing the man being detained by investigators in the departure area of Dover ferry port, which was temporarily evacuated.

In connection with the arrest, police raided the Sunbury-on-Thames home of a respected foster couple.

It is this home which the person in the CCTV footage has just left.

Residents in Cavendish Road were forced to evacuate as police raided the address of Penelope and Ronald Jones on Saturday.

The pair were awarded MBEs in 2009 for services to children and families, and are said to have fostered up to 300 children over 40 years.

The 71 and 88-year-old were described as "beautiful people" by neighbours.

One person labelled them great pillars of the community", adding: "They do a job that not many people do."

Investigations at the home remained underway on Sunday.

A police cordon at an addressed searched in Sunbury-on-Thames. Credit: PA

On Sunday, Scotland Yard arrested a second man in connection with the investigation.

Police said a 21-year-old man was arrested in Hounslow shortly before midnight, and was detained under section 41 of the Terrorism Act.

The Metropolitan Police said it was searching a residential address in Stanwell, Surrey, in conjunction with this arrest.

Police made one arrest outside of a Hounslow chicken shop.

One of the chicken shop owners said Farroukh had been an employee at Aladdins preparing food - and was arrested following a shift.

Describing Farroukh, Suleman Sarwar said: "Normal. Just like how you get on with your colleagues. Very normal.

"If he did do anything you would have never suspected it."

Mr Suleman added: "There's nothing particular that will stand out to stay what made him different."

He said he believed Farroukh was a refugee from Syria.

Of the 30 people injured in the bombing, all but one have been discharged from hospital, with a remaining patient being treated at Chelsea and Westminster Hospital, which has a specialist burns unit.

The UK's terror threat level was downgraded on Sunday from critical - meaning an attack is imminent - to severe, meaning an attack is highly likely.

Making the announcement, Home Secretary Amber Rudd said the police had made "good progress" in the investigation, while also urging the public to "continue to be vigilant but not alarmed".

The threat level has been downgraded from critical to severe. Credit: PA

Metropolitan Police Assistant Commissioner Mark Rowley added that the investigation into the bombing was continuing at a "rapid" pace, and that authorities "are getting a greater understanding of the preparation of the device".

He continued that the "progress" made in the investigation had led to the downgrading of the threat level.

Mr Rowley added that while the terror threat level had been downgraded, "for practical and precautionary reasons" there were be an increased level of policing, with assistance from the military, into the beginning of this week.