A man remains in police custody following his arrest by a counter-terrorism unit investigating threats made to officers.
The 31-year-old man was arrested yesterday at a property in the West Midlands.
Bosses at West Midlands Police called their officers and staff in to special briefings on Monday night and security measures were stepped up after the force received an anonymous tip-off.
Police have not confirmed the specific details of the case, but did not deny reports that there had been a threat to kidnap and kill a police officer.
Assistant Chief Constable Garry Forsyth said the force takes any threat to its officers' safety seriously but added that it is "business as usual" with officers continuing in their normal frontline duties.
He said: "It's really important to stress there is no information we've received that indicates any threat to the public, and this relates purely to officers and staff.
"We've taken appropriate measures to ensure our staff have the information they need to continue to provide the business they do, day in and day out.
"But in terms of specific information that's not something I'll talk about in detail."
The briefings advised officers not to come to work or go off shift in uniform, and also included a reminder about basic police station security measures.
Mr Forsyth said every officer on operational duty had been given "basic and fundamental security advice", adding that otherwise it was "no different to any other day".
Metropolitan Police Commissioner Sir Bernard Hogan-Howe said the force had spoken with their colleagues in the West Midlands and believed they had received the tip-off through "an anonymous call".
He said the Met had not given any guidance to its own officers, but was monitoring the situation.
Steve White, chairman of the Police Federation of England and Wales (PFEW), said officers faced a daily threat and it was only right that counter terror measures were regularly reviewed.
"We need to be regularly assessing what we do and the changing issues officers have to face on a day-to-day basis," said Mr White.
In October the threat level to police officers across the country was raised to substantial, meaning a targeted attack is a strong possibility.
The national security level remains at severe, meaning a terrorist attack is highly likely.
This latest security alert comes after five men were charged in October with plotting to kill police officers or soldiers on the streets of London.