British police had already been preparing for the possibility of an attack of the kind seen in Paris, the Metropolitan Police's Assistant Commissioner has said.

"It's one of the scenarios we had been thinking about," Mark Rowley, Assistant Commissioner of the Metropolitan Police, told the Today programme.

"In July this year we did a massive exercise in London for exactly this type of scenario - a multiplicity of firearms attacks. We have been planning for it.

"It is very much on the radar in terms of something we think may happen, but of course we constantly hope it won't and all police and intelligence agencies across the Western world are trying to defeat it, but we know that there are people out there trying to do that."

Mr Rowley said the British public may notice changes to policing around ports, streets and major events following multiple attacks in Paris which have left at least 127 people dead.

In pictures: Paris attacks Show all 25 1 /25 In pictures: Paris attacks In pictures: Paris attacks Paris attacks French police with protective shields walk in line near the Bataclan concert hall Reuters In pictures: Paris attacks Paris attacks Rescuers evacuate an injured person on Boulevard des Filles du Calvaire AFP In pictures: Paris attacks Paris attacks French Vigipirate troops mobilize next to Place de la Bastille AFP In pictures: Paris attacks Paris attacks French soldiers mobilize near to the Place de la Bastille AFP In pictures: Paris attacks Paris attacks Wounded people are evacuated outside the scene of a hostage situation at the Bataclan theatre EPA In pictures: Paris attacks Paris attacks People react as they gather to watch the scene near the Bataclan concert hall Reuters In pictures: Paris attacks Paris attacks French police secure the area outside a cafe near the Bataclan concert hall Reuters In pictures: Paris attacks Paris attacks Rescuers workers evacuate victims near the Bataclan concert hall AFP In pictures: Paris attacks Paris attacks French Prime Minister Manuel Valls and French President Francois Hollande attending an emergency meeting at the Interior Ministry AFP In pictures: Paris attacks Paris attacks Spectators invade the pitch of the Stade de France after explosions were heard outside AP In pictures: Paris attacks Paris attacks A man lies on the ground as French police check his identity near the Bataclan concert hall Reuters In pictures: Paris attacks Paris attacks Police officers man a position close to the Bataclan theatre AFP In pictures: Paris attacks Paris attacks Wounded people are evacuated from the Stade de France in Paris EPA In pictures: Paris attacks Paris attacks Two men evacuate the Place de la Republique square in Paris as a police officer looks on AFP In pictures: Paris attacks Paris attacks Football fans are evacuated from the Stade de France stadium In pictures: Paris attacks Paris attacks An armed police officer Dan Gabriel In pictures: Paris attacks Paris attacks The Stade de France is evacuated after reports of an explosion In pictures: Paris attacks Paris attacks A member of the French fire brigade aids an injured individual near the Bataclan concert hall In pictures: Paris attacks Paris attacks Wounded people are evacuated from the Stade de France in Paris In pictures: Paris attacks Paris attacks Police are seen outside a cafe in 10th arrondissement of the French capital Paris, In pictures: Paris attacks Paris attacks Rescuers assist an injured man on Boulevard des Filles du Calvaire, close to the Bataclan concert hall AFP In pictures: Paris attacks Paris attacks The scene at a restaurant in 10th arrondissement In pictures: Paris attacks Paris attacks The Bataclan theatre - where around 100 people are thought be held hostage In pictures: Paris attacks Paris attacks The Stade de France as it was evacuated In pictures: Paris attacks Paris attacks Forensic experts inspect the site of an attack outside the Stade de France stadium in Saint-Denis AFP

"We are doing things like strengthening our policing of ports, we have been strengthening policing on the streets. We have put out some guidance across the country."

He said the current threat level of "severe", which indicates an international terrorist attack is likely, is "the second highest level it can be and the highest it can effectively be for a sustained period".

The threat level was raised in August last year following the rise of Isis.

He added: "At the heart of the success of countering terrorism is the relationship between the public and the police and it needs to be stronger than ever.

"We have had more reports than ever before of behaviour of concern and individuals of concern over the last year or so and we need that to continue.