Sergei Skripal was poisoned by agents of the same shadowy but buccaneering Russian intelligence agency he served in and betrayed decades ago, British authorities have claimed.

Alexander Petrov and Ruslan Boshirov, named as suspects in his attempted murder and of his daughter Yulia in Salisbury, are agents of the GRU, the Russian ministry of defence’s elite intelligence and special forces arm, Theresa May told the House of Commons on Wednesday.

There is barely any information available about the pair, but they are almost certainly commissioned Russian military officers highly trained in covert operations, espionage and assassination.

After releasing photographs of the two well-built men in their…