From Sky News
Russia will not review investments by British firms despite the tense diplomatic row sparked by the murder of Alexander Litvinenko.
Moscow has warned Britain it faces "serious consequences" following the expulsion of four diplomats and is expected to make a statement this afternoon.
Gordon Brown insisted he would give "no apologies" for the move - which comes after Russia refused to hand over the man accused of murdering Mr Litvinenko in London.
Britain was "not prepared to allow a situation of lawlessness to develop in London as a result of a failure to act," the Prime Minister said.
The expulsions were part of a raft of measures announced by Foreign Secretary David Miliband in response to the Kremlin's decision to block the extradition of Andrei Lugovoy, who, like his alleged victim, is another ex-KGB agent .
He said there was a "significant body of evidence" against Lugovoy and the measures would send a "clear and proportionate" signal to Moscow that it should send him to Britain where he would go on trial.
But the Russian government condemned the move as "provocative and immoral" and said it would have the "most serious consequences for Russian-British relations as a whole".
Foreign Ministry spokesman Mikhail Kamynin said the UK was "trying to justify" its own refusal to extradite tycoon Boris Berezovsky and Chechen separatist leader Akhmed Zakayev.
He did not specify what measures Russia would take, but said they would seek to resolve the issues "in a constructive way, without politicising them".
Mr Litvinenko, a former Russian security agent who fled to Britain, died in a London hospital last November after being poisoned with the radioactive isotope polonium 210.
A European arrest warrant has been issued for Lugovoy and a "red alert" put out by Interpol, meaning he could be extradited to the UK if he travels outside Russia.
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