Brokers will be forced to manually enter FSA returns because of the regulator's failure to develop a system-to-system solution.
Larger brokers will be hit the hardest as they will be looking to report using an electronic data feed linking their systems to the FSA's.
Gary Izatt of compliance expert Navigant Consulting said: "Everyone will have to use the FSA's web-based browser and enter data manually.
"It will be an awkward situation for the big brokers."
The FSA originally said it would have the data feed in place by July 2005. But owing to problems with the XBRL reporting standard that was originally proposed, the FSA has conceded it will not be ready.
The regulator has yet to decide whether to continue with XBRL.
The lack of clarity from the FSA is preventing software houses from developing their own system-to-system reporting software.
SSP development and compliance manager, e-business, Gina Cook said: "Until we know for definite what the FSA wants we cannot develop our own proprietary software."
An FSA spokesman said the regulator was still looking at which standard to use.
"It would not be advantageous to go for a system-to-system approach that doesn't work. We are not going to use XBRL until we have evaluated it more."