The man identified as Zabi-ul-Taifi was arrested along with six other militants in a pre-dawn raid on the house of an Afghan refugee on the outskirts of the northwestern city of Peshawar.
"Taifi is among those arrested today," an intelligence official said, on condition of anonymity. Taifi came from the Saudi city of Taif, he said.
The intelligence officials had earlier said that the arrested men were believed to have planned attacks on trucks taking supplies to Western forces in Afghanistan and they included four Arabs and three Afghans. A militant source had said that two Arabs and five Afghans were arrested.
The intelligence officials later said the nationality of the other suspects was being established.
A resident of Bara Qadeem, the village where the raid took place, told Reuters that he saw some "goras", a term usually applied to white Westerners, observing the raid.
"They came in a black car with tinted glass, but did not take part in the operation," he said, speaking on condition of anonymity.
In the July 7, 2005, bombings, four young British Islamist militants killed 52 people and wounded hundreds when they carried out suicide bombings on three underground trains and a bus in central London.
At least two of the young men were known to have travelled to Pakistan, where investigators believe they made contact with militants.
One intelligence official said Taifi was believed to have been the ‘mastermind’ of the London bombings. He did not elaborate.
Pakistan has arrested and killed hundreds of al Qaeda militants since it joined the US-led campaign against Islamist militancy after the September 11 attacks on the United States in 2001. Many of them were handed over to the United States.
Rashid Rauf, a British militant with al Qaeda links suspected of involvement in a plot to blow up airliners over the Atlantic, was killed along with an Egyptian in a US missile strike in northwestern Pakistan in July, Pakistani security agents said.
The United States carried out about 30 attacks on suspected militants with missiles fired by pilotless drones in Pakistan in 2008, according to a Reuters tally, more than half since the beginning of September.
Pakistan objects to the attacks saying they are a violation of its sovereignty and undermine its efforts to tackle militants.
Pakistan's lawless ethnic Pashtun tribal regions in the northwest on the Afghan border are sanctuaries for al Qaeda and Taliban militants fleeing US forces in Afghanistan.
Many militants took refuge in Pakistani cities and towns and were arrested from there.