"One man has been arrested in West Yorkshire and will be brought to London to be questioned," deputy assistant commissioner Peter Clarke told a news conference in London on Tuesday.
The British police also said it was "very likely" that one of four men suspected of carrying out Thursday's bombings in London died in one of the targeted underground trains.
This comes as police searched five homes in northern England as a significant part of the investigation into the bombings which killed at least 52 people.
"We also have very strong forensic and other evidence that it is very likely one of the men from West Yorkshire died in the explosion at Aldgate," in east London, said Clarke, head of the police anti-terrorist branch.
He said police had evidence linking four men - three from the West Yorkshire area - to the four scenes of the London bombings.
"We also have very strong forensic and other evidence that it is very likely one of the men from West Yorkshire died in the explosion at Aldgate"
Deputy Assistant Commissioner, Anti-Terrorist Branch
Clarke added that the investigation was moving "at great speed".
Detectives from London, together with local officers from West Yorkshire, searched four properties around the city of Leeds and were examining a fifth on Tuesday with warrants issued under the Terrorism Act.
The searches were part of a pre-planned intelligence-led operation, a spokeswoman said.
"The searches are in connection with the terrorist attacks in London on 7 July," she added.
An anti-terrorism police spokeswoman said the searches were thought to be significant. "We will be there for some time," she added.
London police chief Ian Blair told BBC radio the raids were directly connected to the bombings.
Leeds has one of the biggest Muslim populations in Britain. In May 2001, it was one of a series of northern English towns which saw rioting between Asian and white youths blamed on ethnic, religious and racial divisions.
The investigation is said to be the
biggest in English history
Last Thursday's London bombs on the underground railway system and a double-decker bus killed at least 52 people and injured more than 700.
Tuesday's operation was the first reported swoop in what police have described as the biggest crime investigation in English history.
Hundreds of extra officers have been drafted in to help the investigation, which involves examining footage from 2500 closed-circuit television cameras around the capital and assessing information given by about 2000 callers.
Forensic experts are meanwhile attempting to reconstruct the bombs using evidence collected at the scene to give them further clues about the attackers.