LONDON (Reuters) - British police said they had charged a 64-year-old man on Thursday with suspected offences under the National Security Act (NSA) following a counter-terrorism investigation, adding that the charge related to Russia.

Howard Michael Phillips from Harlow, a town to the north of the British capital, was arrested in central London earlier this month, police said in a statement.

He was charged with an offence contrary to section 3 of the NSA which relates to assisting a foreign intelligence service.

The case was not connected to any other recent charges or investigations linked to NSA offences, police said.

Next year, five men are due to go on trial accused of various offences relating to an arson attack on a Ukrainian business in London which British prosecutors say was allegedly paid for by Russian intelligence. One of the suspects is facing two charges under the NSA.

Earlier this month, Britain said it would expel Russia's defence attache, remove diplomatic status from some Russian-linked properties and limit the length of Russian diplomatic visas in response to Moscow's "malign activity".

In response, the Russian embassy in London said the measures were being introduced "under a groundless and somewhat ridiculous pretext".

(Reporting by Sarah Young; editing by Michael Holden and Andrew MacAskill)