Rachel Vahey, who heads pension development at Scottish Equitable, said preparing for A-Day had been a "massive" systems challenge which was being made more difficult by the rash of late regulations from the government.
She said that even the block on recycling of tax-free cash could require up to 500 days of additional IT work by Scottish Equitable, while "other projects have had to take a back seat."
Vahey said, "Although HMRC has generally worked well with Scottish Equitable, ideally we would have wanted the information 12 months earlier, rather than find ourselves now still dealing with new regulations that change the way we work."
She added that HMRC's failure to offer online pension scheme reporting on time was a particular frustration.
"It is a big issue for us. We have had to build a system to provide the right information at the right time, but are now faced with devising a plan for at least the next six months."
Vahey said Scottish Equitable was currently in discussions with the Revenue about how best to collate the required information and send it electronically.
Brian Dingsdale, product conversion manager at Friends Provident, said the uncertainty surrounding regulations meant the firm had been forced to "build towards what we believe are the right answers, but without any certainty".
He said Friends Provident would be forced to dig deep into its sizeable A-Day contingency budget to update its software in light of late changes.
Dingsdale's colleague, Mike Shapland, who is head of IT solutions delivery at Friends Provident, said the firm's ability to respond quickly and make the necessary systems changes demanded by any late regulations was helped by its relationship with Indian outsourcing supplier Wipro.
"Having Wipro to call on gives us the resource to increase a project team at short notice," he said.
"In the case of A-Day, the interpretation of any new legislation is something we tackle in-house. But once we have decided on a course of action and how to build what we need, we can then pass that defined project over to Wipro. It gives us the flexibility we need with regulations arriving so haphazardly."
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