In his statement outside Downing Street, David Cameron said:
"What happened yesterday in Woolwich has sickened us all. On our televisions last night and in our newspapers this morning we have all seen images that are deeply shocking.
"The people who did this were trying to divide us. They should know something like this will only bring us together and make us stronger."
More top news
Storm Imogen - when and where we will see the strongest winds? ITV Weather's Manali Lukha gives the breakdown.
Kate Middleton attended a special service to celebrate the landmark occasion in her first engagement as Honorary Air Commandant
The ISIS execution gang fronted by 'Jihadi John' had two British extremists who learned radical Islam together in London, ITV News reveals.