Police officers stand outside a semi-detached house in High Wycombe, England, after a anti-terror raid (File photo)

Police say the two operations were unrelated.

In the first, two men in their 20s were detained in separate locations in the city of Halifax, 320 kilometers north of London.

A number of premises there and an apartment in north London are being searched as part of that investigation. A police source says the two detainees are being questioned in a London police station about so-called extremist material that could be seen as promoting the ideology of terrorism.

In a separate operation, three men have been arrested in and around Manchester in northwest England. Two are in their early 20s and one is in his early 30s. It is believed the men, whose names have not been disclosed, are being questioned about the disappearance of a terrorism suspect who is thought to have fled the country last month.

In a written statement, Manchester police say it is not believed the men are directly linked to any planned terrorism activity in Britain.

All five individuals are being held under the British Terrorism Act of 2000.

Authorities also say none of those arrested is connected in any way to either of the two London bombings in July 2005.

British anti-terrorism officers have made hundreds of arrests since the September 11, 2001, bombings in the United States, but just a handful have been successfully prosecuted.

Last November, the head of Britain's domestic intelligence agency warned that extremists here were plotting at least 30 different terrorist attacks.