Britain's top envoy to Pakistan has expressed concern that extremists in the UK are receiving guidance from al-Qaeda leaders hiding in Pakistan.
The London bombings on 7 July 2005 left 52 people dead
High Commissioner Robert Brinkley said it was a matter of "huge concern", but praised Pakistan's efforts to help.
Britain is home to a large population of Pakistani immigrants, many of whom have retained links with Pakistan.
A number of young Britons of Pakistani origin have been found to be involved in deadly attacks and plots in Britain.
British intelligence services say many of the July 2005 London bombers and those recently convicted of planning to attack UK targets using fertiliser bombs had links to al-Qaeda leaders in Pakistan.
On Wednesday, US Defence Secretary Robert Gates told a congressional panel in Washington that al-Qaeda had established training camps in Pakistan's tribal areas and had links to "terror cells" in other parts of the world.
Speaking in Peshawar on Thursday, Mr Brinkley said there was concern in Britain that extremists there were in contact with al-Qaeda leaders in Pakistan, "from where they get guidance, ideas and in some cases training for operations".
Militants hold sway along much of the Pakistan-Afghan border
The UK was concerned "that some al-Qaeda leaders are still able to hide in and operate from areas along the [Pakistan-Afghan] border", he told reporters.
He said that Britain had a better understanding of how extremists in Britain got in touch with al-Qaeda leaders following the London bombing.
"This is of huge concern to us. Our top priority is to ensure that it does not happen again," Mr Brinkley was quoted as saying by the Dawn newspaper.
He said Britain was in touch with Pakistan to find and detain terrorists operating from that part of the world. He lauded Pakistan's efforts to hunt down and detain terrorists.
"There has been some success, but the fight is not yet over," he said.
He acknowledged there were negotiations between Britain and Pakistan to agree to an extradition treaty, but said the death penalty in Pakistan was a hurdle.
Mr Brinkley said that each case of extradition would have to be considered on merit and in accordance with the law.
He insisted that Britain would have to be assured that those who were extradited to Pakistan would not face capital punishment.