Police are examining a possible link between those involved in Thursday's attacks and a whitewater rafting trip.
At least two bombers are known to have visited the raft centre
Two of the 7 July bombers rode the rapids at Canolfan Tryweryn, the National Whitewater Centre, in Bala, north Wales weeks before the attack.
Officers believe several people with links to addresses being investigated in relation to the 21 July attack may have also been on a trip at the centre.
But it is not yet clear whether they are the suspected bombers.
Earlier in the week it emerged that Mohammad Sidique Khan and Shehzad Tanweer, who both carried out bombings in London on 7 July, attended a whitewater rafting trip on 4 June at Canolfan Tryweryn.
Photographs showed Khan, who carried out the Edgware Road bombing, raising a two-fingered peace sign, and Tanweer, who bombed Aldgate, leaning forward and appearing to laugh.
New intelligence received by detectives has suggested a possible link between the trip and those responsible for the attempted London bomb attack on 21 July, which targeted three London underground trains and one bus.
Officers believe the trip was attended by several people with links to addresses that are "of interest" in relation to the bombing.
Paul O'Sullivan, director of Canolfan Tryweryn, said they were "quite surprised" to find two potential links to the bombings.
Suspects of failed bombings on 21 July are still at large
"We get a lot of people here - 25,000 rafters. We have no names, all we have been able to do is confirm to police that another group rafted on the same day who were of an Asian/ethnic origin."
Bala councillor Elwyn Edwards said he hoped this development could help police.
"To think that these two groups have come here to plan their vile deeds in London does create great concern," he said.
"If that is true, then the records will be here of the names of the second group as well as the first group. I hope that is true and they catch them as soon as possible."
Earlier in the week, a spokesman for Canolfan Tryweryn said: "Following liaison with the police, we are now able to confirm that customers with the names Sidique Khan and Shehzad Tanweer took part in a whitewater rafting trip on June 4."
Other people who are known to have visited the site include the Manchester United football squad and deputy prime minister John Prescott.