Preparations have been ` ` long and thorough , '' says Jonathan Evans . ` ` The preparations are not an easy task , '' he adds . ` The national threat level at present is assessed to be substantial -- meaning that an attack is a strong possibility -- one notch lower than has been the case for much of the last 10 years , '' said Jonathan Evans , director general of the Security Service , known as MI5 , in an address at Mansion House , the official residence of the mayor of London . Concerns are shifting to a less monolithic but wider threat . British would - be terrorists are ` ` a new and worrying threat ''
Preparations have been ` ` long and thorough , '' says Jonathan Evans . ` ` The preparations are not an easy task , '' he adds . Concerns are shifting to a less monolithic but wider threat . British would - be terrorists are ` ` a new and worrying threat ''