People are being urged to check their travel agents before booking Hajj and Umrah packages after an investigation by trading standards.
Six agents in Harrow and Brent were found to be to be non-compliant with travel regulations after checks by officers.
Harrow Borough Council is calling on people to check they have the right documents and their tour operator is ATOL-protected.
The annual Hajj pilgrimage, in which people travel to Mecca and Medina in Saudi Arabia, ends this week, and is the largest gathering of Muslim people in the world.
Every able-bodied Muslim who can afford it is expected to perform the pilgrimage at least once in their lifetime.
The smaller Umrah pilgrimage can be undertaken at any time of the year.
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