"All five men were arrested on suspicion of preparation of a terrorist act, contrary to section 5 of the Terrorism Act (TACT), 2006. Four men [A-D] are Iranian nationals and were detained under TACT," London’s Metropolitan Police said in a statement.

"The nationality of the fifth man [E] is still being established and he was detained under the Police and Criminal Evidence Act (PACE)," the statement said.

All five men currently remain in police custody.

As part of the investigation, officers are also carrying out searches at a number of addresses in the Greater Manchester, London and Swindon areas in connection with this investigation.

The investigation relates to a suspected plot to target a specific premises.

"Officers have been in contact with the affected site to make them aware and provide relevant advice and support, but for operational reasons, we are not able to provide further information at this time," the statement said.

'Fast-moving Investigation

Commander Dominic Murphy, Head of the Met’s Counter Terrorism Command, said: “This is a fast-moving investigation and we are working closely with those at the affected site to keep them updated."

“The investigation is still in its early stages and we are exploring various lines of enquiry to establish any potential motivation as well as to identify whether there may be any further risk to the public linked to this matter,"  Dominic Murphy said.

The London Metropolitan Police said arrests and search activity was supported by officers from Greater Manchester Police and Wiltshire Police, as well as colleagues from Counter Terrorism Policing from across the country.

In a separate statement, police said three people have been arrested in London as part of a Counter Terrorism Policing investigation.

All three men have been taken into custody.

Police, however, said the investigation was not connected to the arrest of five people.