The Queen has sent a message of sympathy to all those affected by the Manchester terror attack, describing what happened as an “act of barbarity.”

Her Majesty said: “The whole nation has been shocked by the death and injury in Manchester of so many people, adults and children , who had just been enjoying a concert.

“I know I speak for everyone in expressing my sympathy to all who have been affected by this dreadful event and especially to the families and friends of those who have died or were injured.

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“I want to thank the emergency services who have responded with such professionalism and care.

“And I would like to express my admiration for the way the people of Manchester have responded, with humanity and compassion, to this act of barbarity.”

Meanwhile, Prime Minister Theresa May has said the official terror threat level will be assessed throughout the day.

The assessment for international terrorism in the UK currently remains at severe.

– What does that mean?

The severe rating indicates an attack is seen as highly likely.

– How many levels are there?

Severe is the second highest out of five, behind critical which means an attack is expected imminently. The other three levels are substantial (an attack is a strong possibility), moderate (an attack is possible but not likely), and low (an attack is unlikely).

– Who decides the threat level?

An organisation called the Joint Terrorism Analysis Centre. It was established in June 2003 and is based at MI5’s London headquarters. JTac is comprised of representatives from 16 government departments and agencies.

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– How long has the threat level been at severe?

More than two years. It was raised from substantial in August 2014 after the rise of Islamic State.

– How has the threat changed over the years?

The level was first made public in 2006. Since then, it has most often been at the severe level, and not been lower than substantial. The critical level has been put in place twice in the past decade, August 2006 and June 2007. On both occasions the assessment was lowered after a few days.