A Russian military intelligence squad behind the Salisbury Novichok attack is now behaving “with impunity” to wreak chaos around the world, senior Whitehall sources have warned.

Theresa May revealed the GRU, Moscow’s shadowy spy network, had plotted the nerve agent assault on Sergei Skripal on the orders of the Kremlin to “send a message” to other suspected traitors.

The two senior GRU officers dispatched to carry out the attack were named as Alexander Petrov and Ruslan Boshirov – fake identities given to them by the agency, although the men’s real names are understood to be known to British authorities.

Downing Street vowed to do everything in its power to “dismantle” the GRU and warned of further…