(Refiles March 13 story to restore dropped words, fix syntax in paragraph 5.)

MOSCOW/LONDON (Reuters) - Russia threatened on Tuesday to expel all British media after Britain warned it could strip Russian broadcaster RT of its UK operating license if the government finds Moscow was behind a chemical attack on a Russian ex-double agent in England.

A British-Russian war of words escalated after London gave Russia until midnight on Tuesday to explain how a Soviet-era nerve agent was used against former spy Sergei Skripal and his daughter Yulia earlier this month.

Britain’s media regulator said RT (Russia Today) could lose its UK license if Prime Minister Theresa May’s government determines Moscow was behind the poisoning.

The state-run RIA news agency cited Russian Foreign Ministry spokeswoman Maria Zakharova as saying in response. “Not a single British media outlet will work in our country if they shut down Russia Today.”

RT is a 24-hour news network funded by Vladimir Putin’s government to air news for viewers who want to “question more”. Some British lawmakers have said RT should be barred from Britain after the poisoning.

Zakharova, speaking on Rossiya 1 state TV, also warned Britain’s government that nobody should threaten a nuclear power, particularly in light of remarks made by Putin earlier this month.

Putin, ahead of an election this weekend he is almost sure to win, announced an array of new nuclear weapons in one of his most bellicose speeches in years, saying they could hit almost any point in the world and evade a U.S.-built missile shield.

Zakharova dismissed a session of Britain’s parliament on the poisoning as a show. “No one can go to a parliament of their country and say: I give Russia 24 hours,” Zakharova told RIA.

“When an foreign affairs body of a country is headed by people who have absolutely nothing to do with foreign policy, who built their career on populism..., it is normal for them to come out and start scare-mongering. Do not (try to) scare us,” she said, apparently referring to British Foreign Secretary Boris Johnson.

Ofcom, which enforces the broadcasting code in Britain, is charged with checking that holders of licenses are “fit and proper”. It said on Tuesday any ruling that Russia had acted unlawfully against Britain over the poisoning would be taken into consideration when assessing RT’s status.

RT, which runs eight TV channels including RT UK broadcast from London, said it disagreed with the position taken by Ofcom.

“Our broadcasting has in no way changed this week from any other week and continues to adhere to all standards,” it said in a statement. “By linking RT to unrelated matters, Ofcom is conflating its role as a broadcasting regulator with matters of state.”

Available in more than 100 countries, RT says it covers stories overlooked by the mainstream media and provides alternative perspectives on current affairs, including giving a Russian viewpoint.

May was to brief Britain’s parliament on the situation on Wednesday and Ofcom said it would consider the implications for RT’s broadcast licenses after that.

In a letter to ANO TV Novosti, the holder of RT’s UK broadcast licenses, Ofcom said it would carry out an independent “fit and proper” assessment and would write to RT again shortly to set out the details of the process.

“This letter explained that, should the UK investigating authorities determine that there was an unlawful use of force by the Russian State against the UK, we would consider this relevant to our ongoing duty to be satisfied that RT is fit and proper,” Ofcom said.