Edgware Road bomber Mohammad Sidique Khan reportedly knew suicide bombers Omar Sharif and Asif Hanif, who blew up an Israeli bar in April 2003.
The claim was made by Manchester businessman Kursheed Fiaz, who was visited by the trio in summer 2001.
Fifty-two people died and hundreds were hurt in the 7 July 2005 London attacks.
In the Israeli attack Londoner Hanif, 21, killed three people and injured 55 by blowing himself up at Mike’s Place in Tel Aviv.
Sharif, 27, of Derby, is thought to have fled after explosives strapped to his body failed. His body was found in the sea 10 days later. He had drowned.
Mr Fiaz’s evidence, which he has not told police about, raises the possibility that Khan, a former teaching assistant from Leeds, was radicalised well before previously realised.
Mr Fiaz, in the documentary Britain’s First Suicide Bombers, said Khan came initially to his offices with Sharif and then with Hanif to encourage young Muslims in “the new ways of Islam”.
However, the young men they tried to recruit became wary when Khan mentioned Afghanistan and Syria, he said.
“The impression we got was that they were looking for some gullible people,” Mr Fiaz said.
“What they tried to do is separate them from our side of it and perhaps give them different ideas.
“The youngsters that are involved with my organisation were told by Sidique Khan that to learn the new ways of Islam you may be asked to go to Pakistan. The lads said ‘yeah, and we’ll have a holiday as well’.
“But then the names such as Afghanistan and Syria were mentioned, so at that stage the lads asked what was going on.”
The programme suggests Mr Khan had connections in Afghanistan, a base for al-Qaeda, before 11 September 2001.
Mr Fiaz was later to realise that all three had become, or wanted to be, suicide bombers.
Khan, 30, blew up the Circle Line underground train near Edgware Road on 7 July, killing himself and six others.
The documentary said Israeli authorities had confirmed Khan had visited Israel on 19 February, 2003 for a 24-hour stay – seven weeks before Sharif and Hanif’s attack.
It also uncovers further information about Sharif, including the extent of his connections with cleric Abu Hamza, the al-Muhajiroun organisation, his involvement in the Afghan war and high level contacts with Hamas.
It said Sharif attended Finsbury Park mosque and listened to radical cleric Abu Hamza and Omar Bakri, the former leader of al-Muhajiroun.
Security analyst Sajjan Gohel told the BBC that the apparent ties highlighted in the programme pointed to “common recruitment tactic” targeting people to join a terrorist group.
Britain’s First Suicide Bombers will air on BBC Two on Tuesday, 11 July at 2100 BST.
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