Muktar Said Ibrahim, 29, spent two months in Pakistan at the same time as Mohammed Siddique Khan and Shehzad Tanweer, Woolwich Crown Court heard.
The explosives Ibrahim made for the second attack on London's transport system had only been seen by the British authorities on one other occasion - 7 July, the jury was told.
Allegations surrounding the link between the two plots were revealed yesterday after reporting restrictions were lifted.
The accusation came from the defence barrister representing co-defendant Manfo Kwaku Asiedu, who broke ranks with the five other suspects to describe how Ibrahim wanted to carry out something "bigger and better than 7/7".
Ibrahim was accused of booby-trapping a 12-storey tower block as well as making the rucksack "bombs". Asiedu, 33, is now seated separately in the dock as a "protective measure".
Stephen Kamlish QC said he had documentary evidence proving Ibrahim, Khan and Tanweer were all in Pakistan at the same time.
Ibrahim, 29, of Stoke Newington, north London, is one of six men accused of taking part in a Muslim plot to carry out murderous suicide bombings on the London transport system.
They all deny charges of conspiracy to murder and conspiracy to cause explosions likely to endanger life.