Two of the bombers on the run after the failed 21 July attacks are believed to have been at a white-water rafting centre in Snowdonia on 4 June at the same time as two of the 7 July suicide bombers, Shahzad Tanweer and Mohammad Sidique Khan.
The growing evidence of direct links between the two units has provoked fears that there could be other bombing cells at large.
The disclosure comes as a fifth bomb was discovered dumped in bushes in London, which contained homemade explosives similar to those used in the previous eight devices.
Three men have been arrested in connection with the attempted attacks in London last Thursday, but despite reports that one of the bombers had been caught, it appears that all four are still on the run.
A massive manhunt is continuing in which the police and security services are working around the clock to locate the failed bombers, amid fears that some will strike again. Evidence has started to emerge that suggests the cell had connections with east Africa, in particular Ethiopia and Somalia.
Police are believed to have identified all four of the would-be bombers, whose explosives failed to detonate on three Tube trains and a bus. The names of two of the terrorists are understood to be among the names of a group of people who went to the National White Water Centre, at Canolfan Tryweryn, near Bala, on 4 June. On the same day, Khan, 30, and Tanweer, 22, both from Leeds, were also at the centre. Photographs of the pair enjoying white-water rafting were later published by the media.
Detectives are investigating whether the named suspects are the same people who carried out the failed attack in London on 21 July. If all four terrorist were at the adventure centre at the same time, the police will want to discover whether they were meeting to discuss the forthcoming terrorist campaign, or linking up with a bomb-maker or al-Qa'ida planner.
The discovery that the units both used a similar-looking type of chemical explosive, both targeted three Tube trains and a bus, and were prepared to carry out suicide attacks in London, points towards some form of co-ordinated operation.
Anti-terrorism sources said yesterday that they were keeping an open mind, but admitted that the involvement of a wider network looked increasingly likely.
The remote rafting centre in north Wales, which attracts 80,000 visitors a year, would have made an ideal meeting place for the bombers, being far away from London and difficult for surveillance teams to go unnoticed.
The photographs showed Khan, who is thought to be the senior member of the suicide bombing team, and Tanweer, plunging through the white water during what was described as a bonding session for the two men. The picture, which was taken just a few weeks before the attacks, shows Khan, the Edgware Road bomber, raising a two-fingered peace sign as he paddles down the river. Tanweer, the Aldgate bomber, is shown leaning forward and laughing.
The managing director of the centre, Paul O'Sullivan, said yesterday that there was nothing to link the two groups, which had booked separately but rafted on the same day. He said none of the men would have spent more than two hours there. A statement from the centre said that as well as the raft containing Khan and Tanweer, "a further group of rafters of a similar ethnic origin also took part in a rafting trip on the afternoon of 4 June".
A 40-minute rafting session on the river Tryweryn costs £25 per person. A two-hour session costs up to £280 per group. Up to seven people can board the 14ft inflatable boats.
Sally Jackson, who runs JJ Canoeing Centre in nearby Llangollen, said that her business partner Jim James had also been visited by police investigating the bombers. She said it was relatively unusual for groups of young Asian men to participate in the sport.
Meanwhile, more details were emerging about the four bombers on the run following the failed attacks last Thursday at Oval, Warren Street and Shepherd's Bush Underground stations, and on a bus in Hackney Road.
Information recovered from three of the rucksack bombs led the police to three addresses in London. One was at a block of flats in Tulse Hill, south London, where the Brazilian man, Jean Charles de Menezes, 27, was living. Mr de Menezes, who stayed in one of about 10 flats at the purpose-built block, was followed by police on Friday morning and shot dead after reportedly fleeing armed officers who confronted him at Stockwell Tube station in south London.
The dead man, who is thought to have been living on a visa in Britain legally, but working illegally as an electrician, lived at flat 17. Police later raided flat 21, where neighbours said three men of Somalian and Ethiopian origin lived. One neighbour said yesterday: "They did not talk to people here, especially women. They were devout Muslims, you could hear their prayers through the floor."
One man was arrested on Saturday night after a raid, thought to be at the same building in Tulse Hill, and is being held on suspicion of the commission, instigation or preparation of acts of terrorism under the Terrorism Act 2000.
He was taken to the high-security police station at Paddington Green. Two other men arrested in Stockwell in connection with the attempted attacks on 21 July are still being questioned at the same police station.
Police obtained an extension to the arrest yesterday and can continue to hold the suspects until Wednesday. None of the bombers are thought to be among the three men detained.
A fifth bomb was discovered by a member of the public in bushes at Little Wormwood Scrubs, north-west London, at 10am on Saturday, police disclosed yesterday.
The device contained home-made explosives similar to the other bombs and material found in a flat in Leeds and in a car in Luton left by the suicide attackers.
Police said the latest device had been left, rather than hidden, in the undergrowth, suggesting a terrorist may have abandoned it while fleeing the scene. Deputy Assistant Commissioner Peter Clarke, head of the Anti-Terrorist Branch, said: "The object appears to have been left in the bushes, rather than hidden. Naturally this is a matter of concern, and I would urge the public to remain vigilant and to report any suspicious items or activity."
Meanwhile, relatives of victims from the 7 July attacks yesterday made an emotional visit to the four sites where their loved ones were killed or injured. More than 230 attended a briefing on the investigation with senior police officers.
London Underground said last night that Aldgate Underground station would reopen tomorrow for the first time since it was struck by a suicide bomber. The Metropolitan Line, which had been partly closed since the attack, will also recommence a full service. Other Tube lines remain disrupted in the aftermath of the bombings. All services on the Circle Line are still suspended.Reuse content