The commissioner of the Metropolitan Police has warned a terror attack in the UK is “highly likely” and a matter of "when, not if".

Sir Bernard Hogan-Howe said he cannot promise an attack will not take place, despite being in charge of preventing them.

He said instead that he could offer reassurance by explaining what the police and security services were doing to protect the public.

Speaking of the terrorist atrocities Europe has seen recently, Sir Bernard said: "I feel and understand that fear, and as the police officer in charge of preventing such an attack I know you want me to reassure you.

"I am afraid I cannot do that entirely. Our threat level has been at 'Severe' for two years. It remains there.

"It means an attack is highly likely - you could say it is a case of when, not if."

Explaining the work of the police, he pointed to the number of terror plots that had been foiled since the murder of Lee Rigby in May 2013, including one to murder officers at Shepherd's Bush police station and another to carry out a Lee Rigby-style attack on US soldiers in East Anglia.

He said the relationship between the police, MI5 and MI6 was a "world-beater" which has given the UK an intelligence advantage and said the nation's gun control laws helped make it difficult for terrorists.

The commissioner said: “Now our resilience has increased as all Met officers who carry a gun have been trained to go forward and take the initiative, in the face of a new terrorist threat.

“Meanwhile we are training hundreds of extra officers so they are ready to supplement our numbers during an attack similar to that seen in Paris. This increases overall numbers of firearms officers by 600 to 2800.”

The UK's top officer also said that the "British way of life and culture" made the country hostile to terrorists.

He said the fact most British police are unarmed gave the public a healthier relationship with officers, helping neighbourhood officers become the nation's eyes and ears, and praised the UK's tolerance and acceptance.

Sir Bernard said: “London is a vibrant city. I am especially proud to police it. Hostile to terrorists and a place the world wants to visit and invest in - and rightly so.

“Help us to keep it that way - be our eyes and ears against terror - but also enjoy it. We should be positive and enjoy our freedoms.

“Yes, these can feel like dark and desperate times, I feel that too sometimes, but defeating this terrorism is as much about refusing to be afraid as anything else, refusing to change our beliefs, our values or our way of life.

“We will not become like them, we will not hate, we will not be cowed and because of this they will never win.”