Basu said he stood by Prime Minister Theresa May who said in March there was no other conclusion than that the Russian state was responsible.
Saying Britain's finding has been independently verified, they urged Russian Federation to provide "full disclosure of its Novichok program".
Britain will brief the UN Security Council later Thursday on its latest findings, with the meeting due to open around 11:30 am (1530 GMT). "It's active and it will be countered by a strong worldwide partnership of allies, able to deploy the full range of tools from across our national security apparatus, and ready to reject the Kremlin's brazen determination to undermine the global rules based order". The threat from Russian Federation is real.
Prime Minister Theresa May hinted that Britain would retaliate using "all the tools in our national security apparatus", but it is hard to imagine what it - or any Western power - can do to prevent this kind of attack.
Russian citizens identified as Alexander Petrov and Ruslan Boshirov were charged in absentia by Britain on Wednesday with trying to murder Sergei Skripal and his daughter Yulia with a military-grade nerve agent in England.
"Every Russian intelligence service makes uses of freelance agents in its operations, including those carried out overseas", said Mark Galeotti, an expert on Russia's intelligence and security agencies.More news: Osaka powers into U.S. Open semis by routing Tsurenko
The Kremlin called these accusations "unacceptable".
May's spokesman said the prime minister had spoken to the United States president, Donald Trump, on Tuesday evening, to the Canadian prime minister, Justin Trudeau, on Wednesday, and earlier on Thursday to Angela Merkel, the German chancellor, and the French president, Emmanuel Macron.
The United Kingdom charged two men on Wednesday with the poisoning of Sergei Skripal, a double-agent who formerly served in Russian military intelligence and spied for the West.
Britain said they were poisoned with the Novichok nerve agent developed in Russia, and that it was highly likely the Russian state had tried to murder them.
"What we have learned today is the specific threat from GRU", May said. But there is limited appetite among Britain's European allies for further sanctions against Moscow.
Police said Ms Sturgess and Mr Rowley were later exposed to Novichok after handling a contaminated container, labelled as Nina Ricci Premier Jour perfume.More news: Leaked Images Show What Is Coming From Apple & It's Not Just iPhones
Nebenzia says that for Russian Federation, "the only issue is what kind of ploy London will invent in order to avoid a truly serious rather than a politically motivated investigation of the case.".
REBUTTAL: Yulia Skipral said in May that she and her father had been attacked and were "so lucky to have survived this attempted assassination". The operation, she said, "was nearly certainly approved outside the GRU at a senior level of the Russian state".
The Russian men also face charges of the use and possession of the deadly Soviet-concocted nerve agent Novichok, and causing "grievous bodily harm with intent" to both Yulia Skripal and Bailey.
The Skripals were discovered unconscious on March 4 on a bench in the southern English town of Salisbury.
Det Sgt Nick Bailey also fell ill after responding to the incident in Salisbury.More news: Democrat releases 'confidential' emails as Kavanaugh hearing heats up