|About 75% of the temple was destroyed in the fire|
The fire at Gurdwara Sikh Sangat in Harley Grove, Bow, last March damaged the Grade II listed building and destroyed several Sikh holy books.
Jagmohan Singh said it was "very disappointing" that no arrests had been made despite a £50,000 reward. Police said "extensive inquiries" had been carried out. Mr. Singh said a 40-hour reading of the Sikh holy book, Guru Granth Sahib Ji, to mark the fire will conclude later.
The fire destroyed 75% of the building and caused the roof to collapse. But the temple continued to function from some rooms at the back of the building, which were restored at a cost of £200,000. "Today is a remembrance day and at the same time it is a celebration as, despite the attack, we are holding worship inside the premises," Mr Singh said.
"The Granth has also returned. It was devastating to see the gurdwara and particularly the holy book targeted. "We are very disappointed with the investigation. Nobody has been apprehended and that is more disappointing than having to provide services from a constrained space."
A statement from Tower Hamlets Borough Police said it had conducted "extensive inquiries" and carried out a "thorough CCTV evaluation".
"We wish to reassure the community that everything that can be done is being done and every possible line of inquiry is being pursued.
"The investigation team is in regular contact with the temple committee and liaise with our independent advisory group, whilst providing updates both locally and nationally to the Federation of Sikh Organisations, UK." The temple will make an appeal to Sikhs based in the UK and abroad to help raise £2.5m to rebuild the temple and plans to approach English Heritage for grants.