A senior intelligence official in the eastern city of Lahore confirmed that the man was in custody, but refused to disclose his name, or elaborate on his alleged links to the July 7 attacks.
It came after UK reports that armed police in Pakistan had seized a major al-Qa'ida figure with suspected close links to the bombers.
The Pakistani authorities were already holding at least seven people suspected of links to the four London suicide bombers - three of whom visited the country in the months before the atrocity.
Shehzad Tanweer, 22, Mohammad Sidique Khan, 30, and Hasib Hussain, 18, all travelled to Karachi in southern Pakistan last year.
Intelligence officials there are now trying to determine whether they received training or other assistance from extremist groups.
It has already been claimed that Tanweer met a leader of the outlawed radical group Jaish-e-Muhammad, which is said to have links to al Qaida, while an al-Qa'ida aide has reportedly said he recognises Khan from a "terror summit" held in the tribal areas of Pakistan last year.
The Pakistani authorities have launched a crackdown on radical groups in the wake of the London bombings and have arrested dozens of suspected militants.
While the focus of attention has shifted to Pakistan in recent days, Scotland Yard has continued to concentrate on the investigation back in Britain.
Experts are still trying to identify the type of explosives used by the bombers, while police are ploughing through thousands of CCTV tapes, witness statements and calls to the Anti-Terrorist hotline.
Last night Egyptian officials said a scientist wanted for questioning over the London bombings had no links to the attacks nor to al-Qa'ida.
Magdy el-Nashar, who studied at Leeds University, had been linked to a flat in the city that is being searched by police.
However, an Egyptian Government spokesman said it was "clear" he had no connection to the attacks.Reuse content