A secret internal review has been launched into a Birmingham-based regional counter-terrorism hub which was set up to identify potentially dangerous radicals plotting atrocities.

Scotland Yard’s Assistant Commissioner John Yates, who is the UK’s most senior counter-terrorism commander, has ordered a fresh look at the work of the UK’s four counter-terrorism units, it has emerged.

The move, ordered several months ago, is not linked to the failed Christmas Day bomb attack on Flight 253 over Detroit. The units were opened two years ago in Birmingham, Manchester, Leeds, and London and have since been boosted by several smaller intelligence cells.

But fears have arisen of turf wars erupting between senior officers during fast-moving operations that straddle force boundaries and some experts have called for Scotland Yard to be given powers to take control of any inquiry instead of having to liaise with forces across England and Wales.

Each regional unit employs around 350 detectives who work alongside MI5 and security services worldwide to combat violent extremism, gathering intelligence on those suspected of planning, assisting or funding attacks in both Britain and abroad.

Since being set up, the West Midlands unit has enjoyed a number of key successes, which included the smashing of a terror cell run by Alum Rock fanatic Parviz Khan.

The 39-year-old was jailed for life last year for plotting to kidnap and behead a soldier and shipping equipment to terror groups on the Pakistan-Afghan border. Eight other men were convicted of offences linked to Khan’s plot.

At Birmingham International Airport, Continental Airlines has warned passengers to arrive four hours before departure due to heightened security following the failed Christmas Day bomb attack..

The American airline, which operates a daily eight-hour flight to New York, has asked the estimated 175 passengers per day to allow plenty of time to pass through the strict security checks.

An aviation expert has told the Birmingham Post that airports face making costly essential security improvements.

Kieran Daly, the former editor of internet news service, Air Transport Intelligence, said that a “major expensive upgrade” would be needed to improve existing systems. He said: “In most cases it involves putting in completely new devices and it’s not just a question of improving what is already there.

“Substantial building work and investment is required.”