Four men detained earlier this week in Birmingham, the second largest city in Britain, were charged with terrorism offences on Friday and will appear in a London court later.

Khobaib Hussain, Ishaaq Hussain, Shahid Kasam Khan and Naweed Mahmood Ali were charged with fundraising for terrorist purposes and travelling to Pakistan for terrorist training.

"These charges are in connection with Operation Pitsford, a major counter terrorism investigation that has already seen?8 people charged and appear in court," a West Midlands Police spokesman said.

Police working on a major counter terrorism operation in Birmingham arrested the four people on Tuesday, increasing the arrests in the anti-terror probe to 12.

The police stressed that the latest arrests were pre-planned and not made in response to any immediate threat to public safety.

Meanwhile, the terrorism threat level in England, Wales and Scotland remains unchanged at "substantial", meaning that a terrorist attack is a "strong possibility."